radv/ci: run two jobs in parallel to reduce the execution time

radv/ci: run two jobs in parallel to reduce the execution time

This should bring the overall execution time at around 15 minutes \o/,
but it exposes more issues in the driver:

 - [...].linear_interpolation.no_offset_8_samples (#7220)
 - Timeouts on some dedicated_alloc.image.full.1048577.* tests
 - Timeout on memory.pipeline_barrier.host_read_host_write

More performance improvements should come later, as the load average
remains in the [12, 16] range when running on my machine on a navi22
gets me a 31 load average and a lower execution time by a couple of
minutes.

References: #7220
Signed-off-by: Martin Roukala (né Peres) <martin.roukala@mupuf.org>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19111>