### 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 if (head->has_member(first)) {
		class_names = p_qualified_name.split("::");
		GDScriptParser::ClassNode::Member member = head->get_member(first);
		if (member.type == GDScriptParser::ClassNode::Member::CLASS) {
			result = member.m_class;
		}
	}
	
	for (int i = 1; result != nullptr && i < class_names.size(); i++) {
		String current_name = class_names[i];
		GDScriptParser::ClassNode *next = nullptr;
		if (result->has_member(current_name)) {
			GDScriptParser::ClassNode::Member member = result->get_member(current_name);
			if (member.type == GDScriptParser::ClassNode::Member::CLASS) {
				next = member.m_class;
			}
		}
		result = next;
	}
	return result;
}
bool GDScriptParser::has_class(const GDScriptParser::ClassNode *p_class) const {
	if (head->fqcn.is_empty() && p_class->fqcn.get_slice("::", 0).is_empty()) {
		return p_class == head;
	} else if (p_class->fqcn.begins_with(head->fqcn)) {
		return find_class(p_class->fqcn.trim_prefix(head->fqcn)) == p_class;
	}
	return false;
}
GDScriptParser::ClassNode *GDScriptParser::parse_class(bool p_is_static) {