Add propose-update on release

Signed-off-by: Frantisek Lachman <[email protected]>

Author: lachmanfrantisek

.packit.yaml

@@ -24,3 +24,7 @@ jobs:
     - fedora-30-x86_64
     - fedora-31-x86_64
     - fedora-rawhide-x86_64
+- job: propose_downstream
+  trigger: release
+  metadata:
+    dist-git-branch: fedora-all