prci: increase gating tasks priority
Sometimes the gating tasks (build and jobs) are blocked because of nightly
regression remaining tasks are in progress. The reason is because nightly
regressions are not finished or they are re-triggered during day-time.
Gating tasks are blocked because they have same priority than nightly tasks.
This commit increases gating tasks priority so the testing of pull requests
will not be blocked anymore.
Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>