ci/freedreno: Test with non-redistributable traces

ci/freedreno: Test with non-redistributable traces

Add a job to test with traces that we cannot redistribute, listed in a
separate file. Since those traces might not be accessible by everyone,
this job is created only when the pipeline is triggered by `marge-bot`.

This job is optional because otherwise it could be blocking a merge
request of someone who cannot really debug the issue due to lack of
access to these traces.

The documentation available under `docs/ci` goes into more details
explaining the rationale behind optional traces.

Signed-off-by: Antonio Caggiano <antonio.caggiano@collabora.com>
Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-by: Emma Anholt <emma@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6441>