x11: Only enable _NET_WM_SYNC_REQUEST for OpenGL windows

It doesn't work well with Vulkan, and Vulkan windows may not have the Vulkan flag set in all circumstances, so only enable it if we explicitly know that OpenGL is being requested instead.

src/video/x11/SDL_x11window.c

@@ -534,7 +534,7 @@ bool X11_CreateWindow(SDL_VideoDevice *_this, SDL_Window *window, SDL_Properties
     }
 
     const bool force_override_redirect = SDL_GetHintBoolean(SDL_HINT_X11_FORCE_OVERRIDE_REDIRECT, false);
-    const bool use_resize_sync = !(window->flags & SDL_WINDOW_VULKAN); /* doesn't work well with Vulkan */
+    const bool use_resize_sync = !!(window->flags & SDL_WINDOW_OPENGL); // Doesn't work well with Vulkan
     SDL_WindowData *windowdata;
     Display *display = data->display;
     int screen = displaydata->screen;