### 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
String doc;
	int line = p_line;
	DocLineState state = DOC_LINE_NORMAL;
	while (comments.has(line - 1)) {
		if (!comments[line - 1].new_line || !comments[line - 1].comment.begins_with("##")) {
			break;
		}
		line--;
	}
	String space_prefix;
	if (comments.has(line) && comments[line].comment.begins_with("##")) {
		int i = 2;
		for (; i < comments[line].comment.length(); i++) {
			if (comments[line].comment[i] != ' ') {
				break;
			}
		}
		space_prefix = String(" ").repeat(i - 2);
	}
	while (comments.has(line)) {
		if (!comments[line].new_line || !comments[line].comment.begins_with("##")) {
			break;
		}
		String doc_line = comments[line].comment.trim_prefix("##");
		doc += _process_doc_line(doc_line, doc, space_prefix, state);
		line++;
	}
	return doc;
}
void GDScriptParser::get_class_doc_comment(int p_line, String &p_brief, String &p_desc, Vector<Pair<String, String>> &p_tutorials, bool p_inner_class) {