[Build] Add manual trigger for updateRelease workflow

This allows to re-run that job manually with the latest changes done in
the releng.aggregator repository.

.github/workflows/updateRelease.yml

@@ -2,6 +2,7 @@ name: Update to next release
 on:
   milestone:
     types: [created]
+  workflow_dispatch
 
 jobs:
   update: