tests: plug leaks when running with --trackmem

(using SDL_VIDEO_DRIVER=x11/wayland on Linux)

test/testnative.c

@@ -212,6 +212,12 @@ int main(int argc, char *argv[])
         MoveSprites(renderer, sprite);
     }
 
+    SDL_DestroyTexture(sprite);
+    SDL_DestroyRenderer(renderer);
+    SDL_DestroyWindow(window);
+    SDL_free(positions);
+    SDL_free(velocities);
+
     quit(0);
 
     return 0; /* to prevent compiler warning */