With NVK_DEBUG=push_sync, we signal and immediately wait on a syncobj
to better detect whitch push failed and then print it. However, the
syncobj wait itself isn't enough to check for errors. We have to try
pushing again. Adding an empty push lets us get errors immediately and
print the actually failing pushbuf to stderr.
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27320>
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