### 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
} else {
			member->doc_description = get_doc_comment(doc_comment_line);
		}
	}
#endif 
	if (member->identifier != nullptr) {
		if (!((String)member->identifier->name).is_empty()) { 
#ifdef DEBUG_ENABLED
			List<MethodInfo> gdscript_funcs;
			GDScriptLanguage::get_singleton()->get_public_functions(&gdscript_funcs);
			for (MethodInfo &info : gdscript_funcs) {
				if (info.name == member->identifier->name) {
					push_warning(member->identifier, GDScriptWarning::SHADOWED_GLOBAL_IDENTIFIER, p_member_kind, member->identifier->name, "built-in function");
				}
			}
			if (Variant::has_utility_function(member->identifier->name)) {
				push_warning(member->identifier, GDScriptWarning::SHADOWED_GLOBAL_IDENTIFIER, p_member_kind, member->identifier->name, "built-in function");
			}
#endif
			if (current_class->members_indices.has(member->identifier->name)) {
				push_error(vformat(R"(%s "%s" has the same name as a previously declared %s.)", p_member_kind.capitalize(), member->identifier->name, current_class->get_member(member->identifier->name).get_type_name()), member->identifier);
			} else {
				current_class->add_member(member);
			}
		} else {
			current_class->add_member(member);
		}
	}
}
void GDScriptParser::parse_class_body(bool p_is_multiline) {