### 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
memdelete(codegen.generator);
	return gd_function;
}
GDScriptFunction *GDScriptCompiler::_make_static_initializer(Error &r_error, GDScript *p_script, const GDScriptParser::ClassNode *p_class) {
	r_error = OK;
	CodeGen codegen;
	codegen.generator = memnew(GDScriptByteCodeGenerator);
	codegen.class_node = p_class;
	codegen.script = p_script;
	StringName func_name = SNAME("@static_initializer");
	bool is_static = true;
	Variant rpc_config;
	GDScriptDataType return_type;
	return_type.has_type = true;
	return_type.kind = GDScriptDataType::BUILTIN;
	return_type.builtin_type = Variant::NIL;
	codegen.function_name = func_name;
	codegen.is_static = is_static;
	codegen.generator->write_start(p_script, func_name, is_static, rpc_config, return_type);
	
	
	GDScriptCodeGenerator::Address class_addr(GDScriptCodeGenerator::Address::CLASS);
	
	
	
	for (const GDScriptParser::ClassNode::Member &member : p_class->members) {
		if (member.type != GDScriptParser::ClassNode::Member::VARIABLE) {
			continue;
		}
		const GDScriptParser::VariableNode *field = member.variable;