Removed subscription to auto-merge-bot

As explained in paritytech/up-to-date-action#18, the issue is caused because the `skipped` event is treated as `completed`. Until a better solution is generated, let's remove this event and triggered it only in pushes.

This reverts polkadot-fellows#272

.github/workflows/up-to-date.yml

@@ -4,9 +4,6 @@ on:
   push:
     branches:
       - main
-  workflow_run:
-    workflows: [Auto Merge Bot]
-    types: [completed]
 
 jobs:
   updatePullRequests:
@@ -16,7 +13,7 @@ jobs:
     steps:
       - name: Generate token
         id: generate_token
-        uses: actions/create-github-app-token@v1.9.3
+        uses: actions/create-github-app-token@v1
         with:
           app-id: ${{ secrets.MERGE_APP_ID }}
           private-key: ${{ secrets.MERGE_APP_KEY }}