zink: don't leak swapchain readback semaphores

these are considered usable after the queue goes idle, so add them
back into the cache

Fixes: e9f18f64b9 ("zink: also cache swapchain semaphores")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23033>

src/gallium/drivers/zink/zink_kopper.c

@@ -867,6 +867,9 @@ zink_kopper_present_readback(struct zink_context *ctx, struct zink_resource *res
 
    zink_kopper_present_queue(screen, res);
    error = VKSCR(QueueWaitIdle)(screen->queue);
+   simple_mtx_lock(&screen->semaphores_lock);
+   util_dynarray_append(&screen->semaphores, VkSemaphore, acquire);
+   simple_mtx_unlock(&screen->semaphores_lock);
    return zink_screen_handle_vkresult(screen, error);
 }