### 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
if (!windows[window_id].window_focused) {
				_process_activate_event(window_id, wParam, lParam);
			} else {
				windows[window_id].saved_wparam = wParam;
				windows[window_id].saved_lparam = lParam;
				
				windows[window_id].focus_timer_id = SetTimer(windows[window_id].hWnd, 2, USER_TIMER_MINIMUM, (TIMERPROC) nullptr);
			}
			if (wParam != WA_INACTIVE) {
				track_mouse_leave_event(hWnd);
			}
			return 0; 
		} break;
		case WM_GETMINMAXINFO: {
			if (windows[window_id].resizable && !windows[window_id].fullscreen) {
				
				Size2 decor = window_get_size_with_decorations(window_id) - window_get_size(window_id);
				MINMAXINFO *min_max_info = (MINMAXINFO *)lParam;
				if (windows[window_id].min_size != Size2()) {
					min_max_info->ptMinTrackSize.x = windows[window_id].min_size.x + decor.x;
					min_max_info->ptMinTrackSize.y = windows[window_id].min_size.y + decor.y;
				}
				if (windows[window_id].max_size != Size2()) {
					min_max_info->ptMaxTrackSize.x = windows[window_id].max_size.x + decor.x;
					min_max_info->ptMaxTrackSize.y = windows[window_id].max_size.y + decor.y;
				}
				return 0;
			}
		} break;
		case WM_ERASEBKGND: {