up-to-date action can be activated by auto-merge-bot (polkadot-fellow…

…s#272)

- triggered up-to-date when auto-merge is enabled
- Linked actions so that, when auto-merge is enabled, it will trigger
up-to-date to update every PR (including this one)
- Resolves paritytech/up-to-date-action#14
- Updated `up-to-date` action's version
- This latest change include paritytech/up-to-date-action#17 which stops
the action from updating PRs which are already up to date
- replaced github action for github's own action
- Let's use github's tools when possible as they _should_ be more secure

- [x] Does not require a CHANGELOG entry

---------

Co-authored-by: fellowship-merge-bot[bot] <151052383+fellowship-merge-bot[bot]@users.noreply.github.com>

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

@@ -4,6 +4,9 @@ on:
   push:
     branches:
       - main
+  workflow_run:
+    workflows: [Auto Merge Bot]
+    types: [completed]
 
 jobs:
   updatePullRequests:
@@ -13,11 +16,11 @@ jobs:
     steps:
       - name: Generate token
         id: generate_token
-        uses: tibdex/github-app-token@v1
+        uses: actions/create-github-app-token@v1.9.3
         with:
-          app_id: ${{ secrets.MERGE_APP_ID }}
-          private_key: ${{ secrets.MERGE_APP_KEY }}
+          app-id: ${{ secrets.MERGE_APP_ID }}
+          private-key: ${{ secrets.MERGE_APP_KEY }}
       - name: Update all the PRs
-        uses: paritytech/[email protected].0
+        uses: paritytech/[email protected].1
         with:
           GITHUB_TOKEN: ${{ steps.generate_token.outputs.token }}