ci: Disable pixmark-piano trace on a630 due to GPU hangs.

I haven't reproduced it with just this trace in a loop locally, but it's
blocked some CI jobs with hangs where a few tiles didn't get
rendered.  For example:

https://gitlab.freedesktop.org/mesa/mesa/-/jobs/3314062

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5667>
1 file changed