Add types to automerge.yml

from https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#pull_request we need to specify our `types`

.github/workflows/automerge.yml

@@ -1,6 +1,7 @@
 name: AutoMerge
 on:
   pull_request:
+    types: ['opened', 'synchronize', 'reopened', 'labeled']
   schedule:
     # The cron job is just a fallback.
     # The "stopwatch" functionality that we have implemented should