### Godot version

4.0.beta12

### System information

Windows 11, RTX 3080

### Issue description

When a Window Node is created with it's Transparent flag set to true and Project Settings --> Display --> Window --> Subwindows --> Embed Subwindows is false, the Window has a black background. By cycling the transparent flag from false and back to true again, during runtime, the window's background then becomes transparent. 

### Steps to reproduce

Attempt to create a Non-embedded Subwindow with a transparent background using the appropriate flags. 

### Minimal reproduction project

Note: this project is from Reddit user [gongpha](https://www.reddit.com/user/gongpha/) and his Reddit post [Learning a Godot 4.0 Window node](https://www.reddit.com/r/godot/comments/xr8yxn/learning_a_godot_40_window_node/)

https://github.com/gongpha/godot4-window-test
_THREAD_SAFE_METHOD_
	ERR_FAIL_COND(p_window == p_parent);
	ERR_FAIL_COND(!windows.has(p_window));
	WindowData &wd_window = windows[p_window];
	ERR_FAIL_COND(wd_window.transient_parent == p_parent);
	ERR_FAIL_COND_MSG(wd_window.always_on_top, "Windows with the 'on top' can't become transient.");
	if (p_parent == INVALID_WINDOW_ID) {
		
		ERR_FAIL_COND(wd_window.transient_parent == INVALID_WINDOW_ID);
		ERR_FAIL_COND(!windows.has(wd_window.transient_parent));
		WindowData &wd_parent = windows[wd_window.transient_parent];
		wd_window.transient_parent = INVALID_WINDOW_ID;
		wd_parent.transient_children.erase(p_window);
		if (wd_window.exclusive) {
			SetWindowLongPtr(wd_window.hWnd, GWLP_HWNDPARENT, (LONG_PTR) nullptr);
		}
	} else {
		ERR_FAIL_COND(!windows.has(p_parent));
		ERR_FAIL_COND_MSG(wd_window.transient_parent != INVALID_WINDOW_ID, "Window already has a transient parent");
		WindowData &wd_parent = windows[p_parent];
		wd_window.transient_parent = p_parent;
		wd_parent.transient_children.insert(p_window);
		if (wd_window.exclusive) {
			SetWindowLongPtr(wd_window.hWnd, GWLP_HWNDPARENT, (LONG_PTR)wd_parent.hWnd);
		}
	}
}
void DisplayServerWindows::window_set_max_size(const Size2i p_size, WindowID p_window) {