### 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
AnnotationNode *last_annotation = annotation_stack.back()->get();
		if (last_annotation->applies_to(p_target)) {
			annotations.push_front(last_annotation);
			annotation_stack.pop_back();
		} else {
			push_error(vformat(R"(Annotation "%s" cannot be applied to a %s.)", last_annotation->name, p_member_kind));
			clear_unused_annotations();
		}
#ifdef TOOLS_ENABLED
		if (last_annotation->start_line == doc_comment_line) {
			doc_comment_line--;
		}
#endif 
	}
	T *member = (this->*p_parse_function)(p_is_static);
	if (member == nullptr) {
		return;
	}
	for (AnnotationNode *&annotation : annotations) {
		member->annotations.push_back(annotation);
	}
#ifdef TOOLS_ENABLED
	
	class_doc_line = MIN(class_doc_line, doc_comment_line - 1);
	
	if (has_comment(previous.start_line, true)) {
		member->doc_description = get_doc_comment(previous.start_line, true);
	} else if (has_comment(doc_comment_line, true)) {
		if constexpr (std::is_same_v<T, ClassNode>) {
			get_class_doc_comment(doc_comment_line, member->doc_brief_description, member->doc_description, member->doc_tutorials, true);