### 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
push_warning(p_source, p_code, Vector<String>{ p_symbols... });
	}
#endif
	void make_completion_context(CompletionType p_type, Node *p_node, int p_argument = -1, bool p_force = false);
	void make_completion_context(CompletionType p_type, Variant::Type p_builtin_type, bool p_force = false);
	void push_completion_call(Node *p_call);
	void pop_completion_call();
	void set_last_completion_call_arg(int p_argument);
	GDScriptTokenizer::Token advance();
	bool match(GDScriptTokenizer::Token::Type p_token_type);
	bool check(GDScriptTokenizer::Token::Type p_token_type) const;
	bool consume(GDScriptTokenizer::Token::Type p_token_type, const String &p_error_message);
	bool is_at_end() const;
	bool is_statement_end_token() const;
	bool is_statement_end() const;
	void end_statement(const String &p_context);
	void synchronize();
	void push_multiline(bool p_state);
	void pop_multiline();
	
	void parse_program();
	ClassNode *parse_class(bool p_is_static);
	void parse_class_name();
	void parse_extends();
	void parse_class_body(bool p_is_multiline);
	template <class T>
	void parse_class_member(T *(GDScriptParser::*p_parse_function)(bool), AnnotationInfo::TargetKind p_target, const String &p_member_kind, bool p_is_static = false);
	SignalNode *parse_signal(bool p_is_static);
	EnumNode *parse_enum(bool p_is_static);