### 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
set_last_completion_call_arg(argument_index++);
			ExpressionNode *argument = parse_expression(false);
			if (argument == nullptr) {
				push_error("Expected expression as the annotation argument.");
				valid = false;
				continue;
			}
			annotation->arguments.push_back(argument);
		} while (match(GDScriptTokenizer::Token::COMMA) && !is_at_end());
		pop_multiline();
		consume(GDScriptTokenizer::Token::PARENTHESIS_CLOSE, R"*(Expected ")" after annotation arguments.)*");
		pop_completion_call();
	}
	complete_extents(annotation);
	match(GDScriptTokenizer::Token::NEWLINE); 
	if (valid) {
		valid = validate_annotation_arguments(annotation);
	}
	return valid ? annotation : nullptr;
}
void GDScriptParser::clear_unused_annotations() {
	for (const AnnotationNode *annotation : annotation_stack) {
		push_error(vformat(R"(Annotation "%s" does not precede a valid target, so it will have no effect.)", annotation->name), annotation);
	}
	annotation_stack.clear();
}
bool GDScriptParser::register_annotation(const MethodInfo &p_info, uint32_t p_target_kinds, AnnotationAction p_apply, const Vector<Variant> &p_default_arguments, bool p_is_vararg) {
	ERR_FAIL_COND_V_MSG(valid_annotations.has(p_info.name), false, vformat(R"(Annotation "%s" already registered.)", p_info.name));
	AnnotationInfo new_annotation;
	new_annotation.info = p_info;