### 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
HMODULE user32_lib = LoadLibraryW(L"user32.dll");
	if (user32_lib) {
		win8p_GetPointerType = (GetPointerTypePtr)GetProcAddress(user32_lib, "GetPointerType");
		win8p_GetPointerPenInfo = (GetPointerPenInfoPtr)GetProcAddress(user32_lib, "GetPointerPenInfo");
		winink_available = win8p_GetPointerType && win8p_GetPointerPenInfo;
	}
	if (winink_available) {
		tablet_drivers.push_back("winink");
	}
	if (OS::get_singleton()->is_hidpi_allowed()) {
		HMODULE Shcore = LoadLibraryW(L"Shcore.dll");
		if (Shcore != nullptr) {
			typedef HRESULT(WINAPI * SetProcessDpiAwareness_t)(SHC_PROCESS_DPI_AWARENESS);
			SetProcessDpiAwareness_t SetProcessDpiAwareness = (SetProcessDpiAwareness_t)GetProcAddress(Shcore, "SetProcessDpiAwareness");
			if (SetProcessDpiAwareness) {
				SetProcessDpiAwareness(SHC_PROCESS_SYSTEM_DPI_AWARE);
			}
		}
	}
	memset(&wc, 0, sizeof(WNDCLASSEXW));
	wc.cbSize = sizeof(WNDCLASSEXW);
	wc.style = CS_OWNDC | CS_DBLCLKS;
	wc.lpfnWndProc = (WNDPROC)::WndProc;
	wc.cbClsExtra = 0;
	wc.cbWndExtra = 0;
	wc.hInstance = hInstance ? hInstance : GetModuleHandle(nullptr);
	wc.hIcon = LoadIcon(nullptr, IDI_WINLOGO);
	wc.hCursor = nullptr;
	wc.hbrBackground = nullptr;
	wc.lpszMenuName = nullptr;