### 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
const HashSet<int> &get_unsafe_lines() const { return unsafe_lines; }
	int get_last_line_number() const { return current.end_line; }
#endif
	GDScriptParser();
	~GDScriptParser();
#ifdef DEBUG_ENABLED
	class TreePrinter {
		int indent_level = 0;
		String indent;
		StringBuilder printed;
		bool pending_indent = false;
		void increase_indent();
		void decrease_indent();
		void push_line(const String &p_line = String());
		void push_text(const String &p_text);
		void print_annotation(const AnnotationNode *p_annotation);
		void print_array(ArrayNode *p_array);
		void print_assert(AssertNode *p_assert);
		void print_assignment(AssignmentNode *p_assignment);
		void print_await(AwaitNode *p_await);
		void print_binary_op(BinaryOpNode *p_binary_op);
		void print_call(CallNode *p_call);
		void print_cast(CastNode *p_cast);
		void print_class(ClassNode *p_class);
		void print_constant(ConstantNode *p_constant);
		void print_dictionary(DictionaryNode *p_dictionary);
		void print_expression(ExpressionNode *p_expression);
		void print_enum(EnumNode *p_enum);
		void print_for(ForNode *p_for);
		void print_function(FunctionNode *p_function, const String &p_context = "Function");