### 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
ERR_FAIL_COND(p_source == nullptr);
	if (is_ignoring_warnings) {
		return;
	}
	if (GLOBAL_GET("debug/gdscript/warnings/exclude_addons").booleanize() && script_path.begins_with("res://addons/")) {
		return;
	}
	if (ignored_warnings.has(p_code)) {
		return;
	}
	int warn_level = (int)GLOBAL_GET(GDScriptWarning::get_settings_path_from_code(p_code));
	if (!warn_level) {
		return;
	}
	GDScriptWarning warning;
	warning.code = p_code;
	warning.symbols = p_symbols;
	warning.start_line = p_source->start_line;
	warning.end_line = p_source->end_line;
	warning.leftmost_column = p_source->leftmost_column;
	warning.rightmost_column = p_source->rightmost_column;
	if (warn_level == GDScriptWarning::WarnLevel::ERROR) {
		push_error(warning.get_message() + String(" (Warning treated as error.)"), p_source);
		return;
	}
	List<GDScriptWarning>::Element *before = nullptr;
	for (List<GDScriptWarning>::Element *E = warnings.front(); E; E = E->next()) {