### 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
f->get_buffer((uint8_t *)&data_small.write[0], bytecount_small);
	HICON icon_small = CreateIconFromResource((PBYTE)&data_small.write[0], bytecount_small, TRUE, 0x00030000);
	ERR_FAIL_COND_MSG(!icon_small, "Could not create 16x16 @" + itos(small_icon_cc) + " icon, error: " + format_error_message(GetLastError()) + ".");
	
	int err = 0;
	SetLastError(err);
	SendMessage(windows[MAIN_WINDOW_ID].hWnd, WM_SETICON, ICON_SMALL, (LPARAM)icon_small);
	err = GetLastError();
	ERR_FAIL_COND_MSG(err, "Error setting ICON_SMALL: " + format_error_message(err) + ".");
	SendMessage(windows[MAIN_WINDOW_ID].hWnd, WM_SETICON, ICON_BIG, (LPARAM)icon_big);
	err = GetLastError();
	ERR_FAIL_COND_MSG(err, "Error setting ICON_BIG: " + format_error_message(err) + ".");
	memdelete(icon_dir);
}
void DisplayServerWindows::set_icon(const Ref<Image> &p_icon) {
	_THREAD_SAFE_METHOD_
	ERR_FAIL_COND(!p_icon.is_valid());
	if (icon != p_icon) {
		icon = p_icon->duplicate();
		if (icon->get_format() != Image::FORMAT_RGBA8) {
			icon->convert(Image::FORMAT_RGBA8);
		}
	}
	int w = icon->get_width();
	int h = icon->get_height();
	
	int icon_len = 40 + h * w * 4;
	Vector<BYTE> v;
	v.resize(icon_len);
	BYTE *icon_bmp = v.ptrw();