### 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
Error _create_binary_operator(CodeGen &codegen, const GDScriptParser::BinaryOpNode *on, Variant::Operator op, bool p_initializer = false, const GDScriptCodeGenerator::Address &p_index_addr = GDScriptCodeGenerator::Address());
	Error _create_binary_operator(CodeGen &codegen, const GDScriptParser::ExpressionNode *p_left_operand, const GDScriptParser::ExpressionNode *p_right_operand, Variant::Operator op, bool p_initializer = false, const GDScriptCodeGenerator::Address &p_index_addr = GDScriptCodeGenerator::Address());
	GDScriptDataType _gdtype_from_datatype(const GDScriptParser::DataType &p_datatype, GDScript *p_owner);
	GDScriptCodeGenerator::Address _parse_assign_right_expression(CodeGen &codegen, Error &r_error, const GDScriptParser::AssignmentNode *p_assignmentint, const GDScriptCodeGenerator::Address &p_index_addr = GDScriptCodeGenerator::Address());
	GDScriptCodeGenerator::Address _parse_expression(CodeGen &codegen, Error &r_error, const GDScriptParser::ExpressionNode *p_expression, bool p_root = false, bool p_initializer = false, const GDScriptCodeGenerator::Address &p_index_addr = GDScriptCodeGenerator::Address());
	GDScriptCodeGenerator::Address _parse_match_pattern(CodeGen &codegen, Error &r_error, const GDScriptParser::PatternNode *p_pattern, const GDScriptCodeGenerator::Address &p_value_addr, const GDScriptCodeGenerator::Address &p_type_addr, const GDScriptCodeGenerator::Address &p_previous_test, bool p_is_first, bool p_is_nested);
	void _add_locals_in_block(CodeGen &codegen, const GDScriptParser::SuiteNode *p_block);
	Error _parse_block(CodeGen &codegen, const GDScriptParser::SuiteNode *p_block, bool p_add_locals = true);
	GDScriptFunction *_parse_function(Error &r_error, GDScript *p_script, const GDScriptParser::ClassNode *p_class, const GDScriptParser::FunctionNode *p_func, bool p_for_ready = false, bool p_for_lambda = false);
	GDScriptFunction *_make_static_initializer(Error &r_error, GDScript *p_script, const GDScriptParser::ClassNode *p_class);
	Error _parse_setter_getter(GDScript *p_script, const GDScriptParser::ClassNode *p_class, const GDScriptParser::VariableNode *p_variable, bool p_is_setter);
	Error _populate_class_members(GDScript *p_script, const GDScriptParser::ClassNode *p_class, bool p_keep_state);
	Error _compile_class(GDScript *p_script, const GDScriptParser::ClassNode *p_class, bool p_keep_state);
	int err_line = 0;
	int err_column = 0;
	StringName source;
	String error;
	GDScriptParser::ExpressionNode *awaited_node = nullptr;
	bool has_static_data = false;
public:
	static void convert_to_initializer_type(Variant &p_variant, const GDScriptParser::VariableNode *p_node);
	static void make_scripts(GDScript *p_script, const GDScriptParser::ClassNode *p_class, bool p_keep_state);
	Error compile(const GDScriptParser *p_parser, GDScript *p_script, bool p_keep_state = false);
	String get_error() const;
	int get_error_line() const;
	int get_error_column() const;
	GDScriptCompiler();
};
#endif