ci/deqp: Skip flush_finish on all CI jobs.

ci/deqp: Skip flush_finish on all CI jobs.

They're too slow to run in CI even on non-tiled renderers, they don't
block conformance (unless you crash), and provide unreliable warning
results unless you isolate them from other activity on the system.

This means that the following jobs now skip these tests:

- deqp-iris-*
- deqp-llvmpipe (you know, the one mentioned in the comment!)
- deqp-virgl-gl
- deqp-zink-lvp

Acked-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11333>