### 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
ExpressionNode *parse_lambda(ExpressionNode *p_previous_operand, bool p_can_assign);
	ExpressionNode *parse_type_test(ExpressionNode *p_previous_operand, bool p_can_assign);
	ExpressionNode *parse_yield(ExpressionNode *p_previous_operand, bool p_can_assign);
	ExpressionNode *parse_invalid_token(ExpressionNode *p_previous_operand, bool p_can_assign);
	TypeNode *parse_type(bool p_allow_void = false);
#ifdef TOOLS_ENABLED
	
	int class_doc_line = 0x7FFFFFFF;
	bool has_comment(int p_line, bool p_must_be_doc = false);
	String get_doc_comment(int p_line, bool p_single_line = false);
	void get_class_doc_comment(int p_line, String &p_brief, String &p_desc, Vector<Pair<String, String>> &p_tutorials, bool p_inner_class);
#endif 
public:
	Error parse(const String &p_source_code, const String &p_script_path, bool p_for_completion);
	ClassNode *get_tree() const { return head; }
	bool is_tool() const { return _is_tool; }
	ClassNode *find_class(const String &p_qualified_name) const;
	bool has_class(const GDScriptParser::ClassNode *p_class) const;
	static Variant::Type get_builtin_type(const StringName &p_type);
	CompletionContext get_completion_context() const { return completion_context; }
	CompletionCall get_completion_call() const { return completion_call; }
	void get_annotation_list(List<MethodInfo> *r_annotations) const;
	bool annotation_exists(const String &p_annotation_name) const;
	const List<ParserError> &get_errors() const { return errors; }
	const List<String> get_dependencies() const {
		
		return List<String>();
	}
#ifdef DEBUG_ENABLED
	const List<GDScriptWarning> &get_warnings() const { return warnings; }