Allow formats with alpha channels for window textures

Because the blend mode is explicitly set to SDL_BLENDMODE_NONE, it doesn't matter if there's a transparency channel in the texture format or not for opaque windows. This ensures that a 32-bit format is used with Metal instead of SDL_PIXELFORMAT_RGB565.

(cherry picked from commit b1f390255a239940050f87cfb52dacb796e76728)

src/video/SDL_video.c

@@ -422,7 +422,7 @@ static bool SDL_CreateWindowTexture(SDL_VideoDevice *_this, SDL_Window *window,
             !SDL_ISPIXELFORMAT_10BIT(texture_format) &&
             !SDL_ISPIXELFORMAT_FLOAT(texture_format) &&
             !SDL_ISPIXELFORMAT_INDEXED(texture_format) &&
-            transparent == SDL_ISPIXELFORMAT_ALPHA(texture_format)) {
+            (!transparent || SDL_ISPIXELFORMAT_ALPHA(texture_format))) {
             *format = texture_format;
             break;
         }