### 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
}
				break;
			case GDScriptParser::DataType::CLASS:
				if (ClassDB::is_parent_class(export_type.native_type, SNAME("Resource"))) {
					variable->export_info.type = Variant::OBJECT;
					variable->export_info.hint = PROPERTY_HINT_RESOURCE_TYPE;
					variable->export_info.hint_string = export_type.to_string();
				} else if (ClassDB::is_parent_class(export_type.native_type, SNAME("Node"))) {
					variable->export_info.type = Variant::OBJECT;
					variable->export_info.hint = PROPERTY_HINT_NODE_TYPE;
					variable->export_info.hint_string = export_type.to_string();
				} else {
					push_error(R"(Export type can only be built-in, a resource, a node, or an enum.)", variable);
					return false;
				}
				break;
			case GDScriptParser::DataType::SCRIPT: {
				StringName class_name;
				StringName native_base;
				if (export_type.script_type.is_valid()) {
					class_name = export_type.script_type->get_language()->get_global_class_name(export_type.script_type->get_path());
					native_base = export_type.script_type->get_instance_base_type();
				}
				if (class_name == StringName()) {
					Ref<Script> script = ResourceLoader::load(export_type.script_path, SNAME("Script"));
					if (script.is_valid()) {
						class_name = script->get_language()->get_global_class_name(export_type.script_path);
						native_base = script->get_instance_base_type();
					}
				}