Configure allowed_builders (#848)

Configure allowed_builders

Reviewed-by: Maja Massarini

Author: softwarefactory-project-zuul[bot]

.packit.yaml

@@ -101,6 +101,7 @@ jobs:
   - job: bodhi_update
     trigger: commit
     packit_instances: ["stg"]
+    allowed_builders: ["packit-stg", "packit"]
     dist_git_branches:
       - fedora-latest # branched version, rawhide updates are created automatically
       - fedora-stable