Pin microshift build for openshift-4.18 rc.0

Created by job run https://art-jenkins.apps.prod-stable-spoke1-dc-iad2.itup.redhat.com/job/aos-cd-builds/job/build%252Fbuild-microshift/1451

releases.yml

@@ -16,7 +16,12 @@ releases:
         upgrades: 4.17.5,4.17.6,4.17.7,4.18.0-ec.0,4.18.0-ec.1,4.18.0-ec.2,4.18.0-ec.3,4.18.0-ec.4
       members:
         images: []
-        rpms: []
+        rpms:
+        - distgit_key: microshift
+          why: Pin microshift to assembly
+          metadata:
+            is:
+              el9: microshift-4.18.0~rc.0-202412022121.p0.gc2374ca.assembly.rc.0.el9
       rhcos:
         rhel-coreos:
           images: