### Godot version

v4.0.2.stable.custom_build (nixpkgs version)

### System information

NixOS

### Issue description

The [docs](https://docs.godotengine.org/en/latest/tutorials/scripting/gdscript/gdscript_basics.html#variables) seem to specify that uninitialized variables are null (as noted in this comment on the related issue: https://github.com/godotengine/godot/issues/56223#issuecomment-1175794500):
`var a # Data type is 'null' by default.`

This isn't always the case inside branches within loops. Instead, the variables can take on values from other branches.

### Related
- https://github.com/godotengine/godot/issues/56223

### Steps to reproduce

```
@tool
extends EditorScript

func _run():
	for i in 5:
		if i % 2:
			var j = i
			print("i = %s, j = %s" % [i, j])
		else:
			var k
			print("i = %s, k = %s" % [i, k])
```

Running this prints:
```
i = 0, k = <null>
i = 1, j = 1
i = 2, k = 1
i = 3, j = 3
i = 4, k = 3
```

This version also gives the exact same result:
```
@tool
extends EditorScript

func _run():
	for i in 5:
		match i % 2:
			1:
				var j = i
				print("i = %s, j = %s" % [i, j])
			0:
				var k
				print("i = %s, k = %s" % [i, k])
```

In addition, behavior similar to that described in https://github.com/godotengine/godot/issues/56223#issuecomment-1000996579 can still be reproduced as follows:
```
@tool
extends EditorScript

func _run():
	for i in 3:
		if i % 2:
			for j in range(1, 6, 3):
				pass
			print("i = %s" % i)
		else:
			var k
			var l
			var m
			print("i = %s, k = %s, l = %s, m = %s" % [i, k, l, m])
```
Which prints:
```
i = 0, k = <null>, l = <null>, m = <null>
i = 1
i = 2, k = 4, l = 7, m = (1, 6, 3)
```

### Minimal reproduction project

N/A
register_annotation(MethodInfo("@export_dir"), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_DIR, Variant::STRING>);
	register_annotation(MethodInfo("@export_global_file", PropertyInfo(Variant::STRING, "filter")), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_GLOBAL_FILE, Variant::STRING>, varray(""), true);
	register_annotation(MethodInfo("@export_global_dir"), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_GLOBAL_DIR, Variant::STRING>);
	register_annotation(MethodInfo("@export_multiline"), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_MULTILINE_TEXT, Variant::STRING>);
	register_annotation(MethodInfo("@export_placeholder", PropertyInfo(Variant::STRING, "placeholder")), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_PLACEHOLDER_TEXT, Variant::STRING>);
	register_annotation(MethodInfo("@export_range", PropertyInfo(Variant::FLOAT, "min"), PropertyInfo(Variant::FLOAT, "max"), PropertyInfo(Variant::FLOAT, "step"), PropertyInfo(Variant::STRING, "extra_hints")), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_RANGE, Variant::FLOAT>, varray(1.0, ""), true);
	register_annotation(MethodInfo("@export_exp_easing", PropertyInfo(Variant::STRING, "hints")), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_EXP_EASING, Variant::FLOAT>, varray(""), true);
	register_annotation(MethodInfo("@export_color_no_alpha"), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_COLOR_NO_ALPHA, Variant::COLOR>);
	register_annotation(MethodInfo("@export_node_path", PropertyInfo(Variant::STRING, "type")), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_NODE_PATH_VALID_TYPES, Variant::NODE_PATH>, varray(""), true);
	register_annotation(MethodInfo("@export_flags", PropertyInfo(Variant::STRING, "names")), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_FLAGS, Variant::INT>, varray(), true);
	register_annotation(MethodInfo("@export_flags_2d_render"), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_LAYERS_2D_RENDER, Variant::INT>);
	register_annotation(MethodInfo("@export_flags_2d_physics"), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_LAYERS_2D_PHYSICS, Variant::INT>);
	register_annotation(MethodInfo("@export_flags_2d_navigation"), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_LAYERS_2D_NAVIGATION, Variant::INT>);
	register_annotation(MethodInfo("@export_flags_3d_render"), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_LAYERS_3D_RENDER, Variant::INT>);
	register_annotation(MethodInfo("@export_flags_3d_physics"), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_LAYERS_3D_PHYSICS, Variant::INT>);
	register_annotation(MethodInfo("@export_flags_3d_navigation"), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_LAYERS_3D_NAVIGATION, Variant::INT>);
	register_annotation(MethodInfo("@export_flags_avoidance"), AnnotationInfo::VARIABLE, &GDScriptParser::export_annotations<PROPERTY_HINT_LAYERS_AVOIDANCE, Variant::INT>);
	
	register_annotation(MethodInfo("@export_category", PropertyInfo(Variant::STRING, "name")), AnnotationInfo::STANDALONE, &GDScriptParser::export_group_annotations<PROPERTY_USAGE_CATEGORY>);
	register_annotation(MethodInfo("@export_group", PropertyInfo(Variant::STRING, "name"), PropertyInfo(Variant::STRING, "prefix")), AnnotationInfo::STANDALONE, &GDScriptParser::export_group_annotations<PROPERTY_USAGE_GROUP>, varray(""));
	register_annotation(MethodInfo("@export_subgroup", PropertyInfo(Variant::STRING, "name"), PropertyInfo(Variant::STRING, "prefix")), AnnotationInfo::STANDALONE, &GDScriptParser::export_group_annotations<PROPERTY_USAGE_SUBGROUP>, varray(""));
	
	register_annotation(MethodInfo("@warning_ignore", PropertyInfo(Variant::STRING, "warning")), AnnotationInfo::CLASS | AnnotationInfo::VARIABLE | AnnotationInfo::SIGNAL | AnnotationInfo::CONSTANT | AnnotationInfo::FUNCTION | AnnotationInfo::STATEMENT, &GDScriptParser::warning_annotations, varray(), true);
	
	register_annotation(MethodInfo("@rpc", PropertyInfo(Variant::STRING, "mode"), PropertyInfo(Variant::STRING, "sync"), PropertyInfo(Variant::STRING, "transfer_mode"), PropertyInfo(Variant::INT, "transfer_channel")), AnnotationInfo::FUNCTION, &GDScriptParser::rpc_annotation, varray("authority", "call_remote", "unreliable", 0));
#ifdef DEBUG_ENABLED
	is_ignoring_warnings = !(bool)GLOBAL_GET("debug/gdscript/warnings/enable");
#endif
}
GDScriptParser::~GDScriptParser() {