ci: Add a disabled-by-default job for GLES3 testing on db410c.

ci: Add a disabled-by-default job for GLES3 testing on db410c.

Now that we have 7 (soon 8) boards available, there's capacity to be
testing GLES 3.0.  However, due to (it looks like) buffer overflows in the
driver, we end up with flaky test results: 1/60 jobs spuriously failed,
and another 6/60 jobs reported flakes.  At 6 jobs per pipeline, that's way
too high of a failure rate to enable for non-freedreno developers.  Leave
the job present but disabled so that we can do manual test runs for
regressions.

Reviewed-by: Daniel Stone <daniels@collabora.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3661>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3661>