CI: Add kpet_tree_family to RT check config

This allows us to reuse the RT check for both builds only (merge
request runs) and baseline runs (that include tests).

Being able to run tests for the RT baseline runs allows the RT team to
get rid of the manual step of running the tests after they go through
the trouble of building the kernel.

Upstream Status: RHEL-only
Bugzilla: INTERNAL

Signed-off-by: Veronika Kabatova <vkabatov@redhat.com>

.gitlab-ci.yml

@@ -40,6 +40,7 @@ workflow: !reference [.workflow]
   variables:
     merge_branch: main-rt
     name: kernel-rt-c9s
+    kpet_tree_family: c9s-rt
 
 .realtime_check_rhel9:
   trigger: