Use different repo in gating tmt plan

Change the test source location to support evolving downstream testing
requirements. This is needed both for downstream certification
activities and changes to test development for internal infrastructure
differences.

plans/public.fmf

@@ -1,7 +1,20 @@
-summary: Public (Fedora) beakerlib tests
+summary: Public (CentOS) beakerlib tests
+
+adjust+:
+  - when: distro == centos-stream
+    because: Update all packages and reboot
+    discover+<:
+      - name: update-and-reboot
+        how: shell
+        tests:
+          - name: update
+            test: dnf update --refresh -y
+          - name: reboot
+            test: "[[ $TMT_REBOOT_COUNT == 0 ]] && tmt-reboot || echo Already rebooted"
+
 discover:
-  - name: fedora
+  - name: centos
     how: fmf
-    url: https://src.fedoraproject.org/tests/ruby.git
+    url: https://gitlab.com/redhat/centos-stream/tests/ruby
 execute:
     how: tmt