Merge branch 'el9-igwn/builder' into 'main'

Use igwn/builder:el9-testing image for EL9 build jobs in CI

See merge request !95

.gitlab/ci/rhel.yml

@@ -38,7 +38,7 @@ include:
 
 .el9-builder:
   extends: .el9
-  #image: igwn/builder:el9-testing  <-- igwn/builder isn't ready
+  image: igwn/builder:el9-testing
 
 # -- source packages --------
 #