### 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
new_annotation.info.default_arguments = p_default_arguments;
	if (p_is_vararg) {
		new_annotation.info.flags |= METHOD_FLAG_VARARG;
	}
	new_annotation.apply = p_apply;
	new_annotation.target_kind = p_target_kinds;
	valid_annotations[p_info.name] = new_annotation;
	return true;
}
GDScriptParser::SuiteNode *GDScriptParser::parse_suite(const String &p_context, SuiteNode *p_suite, bool p_for_lambda) {
	SuiteNode *suite = p_suite != nullptr ? p_suite : alloc_node<SuiteNode>();
	suite->parent_block = current_suite;
	suite->parent_function = current_function;
	current_suite = suite;
	bool multiline = false;
	if (match(GDScriptTokenizer::Token::NEWLINE)) {
		multiline = true;
	}
	if (multiline) {
		if (!consume(GDScriptTokenizer::Token::INDENT, vformat(R"(Expected indented block after %s.)", p_context))) {
			current_suite = suite->parent_block;
			complete_extents(suite);
			return suite;
		}
	}
	reset_extents(suite, current);
	int error_count = 0;
	do {
		if (is_at_end() || (!multiline && previous.type == GDScriptTokenizer::Token::SEMICOLON && check(GDScriptTokenizer::Token::NEWLINE))) {
			break;