fix leak of frame_fence in sdlgpu renderer

src/renderer_sdlgpu.c

@@ -287,6 +287,7 @@ void renderer_frame_end() {
 
     SDL_GPUFence *frame_fence = SDL_SubmitGPUCommandBufferAndAcquireFence(render_command_buffer);
     SDL_WaitForGPUFences(device, true, &frame_fence, 1);
+    SDL_ReleaseGPUFence(device, frame_fence);
 
     copy_command_buffer   = SDL_AcquireGPUCommandBuffer(device);
     render_command_buffer = SDL_AcquireGPUCommandBuffer(device);