Use arcade backport workflow (#8683)

Author: mmitche

.github/workflows/backport.yml

@@ -2,53 +2,17 @@ name: Backport PR to branch
 on:
   issue_comment:
     types: [created]
+  schedule:
+    # once a day at 13:00 UTC to cleanup old runs
+    - cron: '0 13 * * *'
 
-permissions: {}
+permissions:
+  contents: write
+  issues: write
+  pull-requests: write
+  actions: write
 
 jobs:
   backport:
-    if: github.event.issue.pull_request != '' && contains(github.event.comment.body, '/backport to') && contains(fromJSON('["OWNER", "MEMBER", "COLLABORATOR"]'), github.event.comment.author_association)
-    runs-on: ubuntu-24.04
-    permissions:
-      contents: write
-      issues: write
-      pull-requests: write
-
-    steps:
-    - name: Extract backport target branch
-      uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd
-      id: target-branch-extractor
-      with:
-        result-encoding: string
-        script: |
-          if (context.eventName !== "issue_comment") throw "Error: This action only works on issue_comment events.";
-
-          // extract the target branch name from the trigger phrase containing these characters: a-z, A-Z, digits, forward slash, dot, hyphen, underscore
-          const regex = /\/backport to ([a-zA-Z\d\/\.\-\_]+)/;
-          target_branch = regex.exec(context.payload.comment.body);
-          if (target_branch == null) throw "Error: No backport branch found in the trigger phrase.";
-
-          return target_branch[1];
-    - name: Post backport started comment to pull request
-      uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd
-      with:
-        script: |
-          const backport_start_body = `Started backporting to ${{ steps.target-branch-extractor.outputs.result }}: https://github.com/${context.repo.owner}/${context.repo.repo}/actions/runs/${process.env.GITHUB_RUN_ID}`;
-          await github.rest.issues.createComment({
-            issue_number: context.issue.number,
-            owner: context.repo.owner,
-            repo: context.repo.repo,
-            body: backport_start_body
-          });
-    - name: Checkout repo
-      uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8
-      with:
-        persist-credentials: true # We need to persist credentials to push the resulting changes upstream.
-        fetch-depth: 0
-    - name: Run backport
-      uses: ./eng/actions/backport
-      with:
-        target_branch: ${{ steps.target-branch-extractor.outputs.result }}
-        auth_token: ${{ secrets.GITHUB_TOKEN }}
-        exclude: 'documentation/**.md'
-        label: backport
+    if: ${{ contains(github.event.comment.body, '/backport to') || github.event_name == 'schedule' }}
+    uses: dotnet/arcade/.github/workflows/backport-base.yml@main