### 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
ERR_FAIL_COND_V_MSG(p_node->type != Node::VARIABLE, false, vformat(R"("%s" annotation can only be applied to variables.)", p_annotation->name));
	VariableNode *variable = static_cast<VariableNode *>(p_node);
	if (variable->is_static) {
		push_error(vformat(R"(Annotation "%s" cannot be applied to a static variable.)", p_annotation->name), p_annotation);
		return false;
	}
	if (variable->exported) {
		push_error(vformat(R"(Annotation "%s" cannot be used with another "@export" annotation.)", p_annotation->name), p_annotation);
		return false;
	}
	variable->exported = true;
	variable->export_info.type = t_type;
	variable->export_info.hint = t_hint;
	String hint_string;
	for (int i = 0; i < p_annotation->resolved_arguments.size(); i++) {
		String arg_string = String(p_annotation->resolved_arguments[i]);
		if (p_annotation->name != SNAME("@export_placeholder")) {
			if (arg_string.is_empty()) {
				push_error(vformat(R"(Argument %d of annotation "%s" is empty.)", i + 1, p_annotation->name), p_annotation->arguments[i]);
				return false;
			}
			if (arg_string.contains(",")) {
				push_error(vformat(R"(Argument %d of annotation "%s" contains a comma. Use separate arguments instead.)", i + 1, p_annotation->name), p_annotation->arguments[i]);
				return false;
			}
		}
		if (p_annotation->name == SNAME("@export_flags")) {
			const int64_t max_flags = 32;
			Vector<String> t = arg_string.split(":", true, 1);
			if (t[0].is_empty()) {