[TASK] Migrate backport to shared reusable workflow

[CybotTM]

Summary

blog_example was the last TYPO3-Documentation repo still referencing the broken m-kuhn/backport@30b6e83 action (missing dist/index.js — the original bug that started the shared-workflows initiative). This replaces it with the org shared reusable-backport.yml, matching the 9 already-migrated repos.

Change

-    steps:
-      - name: Backport
-        uses: m-kuhn/backport@30b6e83...   # BROKEN — missing dist/index.js
-        with:
-          github_token: ${{ secrets.GITHUB_TOKEN }}
+    uses: TYPO3-Documentation/.github/.github/workflows/reusable-backport.yml@main
+    with:
+      label_pattern: "^backport (.+)$"
+    secrets:
+      APP_ID: ${{ secrets.APP_ID }}
+      APP_PRIVATE_KEY: ${{ secrets.APP_PRIVATE_KEY }}

⚠️ One thing a maintainer must confirm

The shared workflow generates a GitHub App token from APP_ID / APP_PRIVATE_KEY (so backport PRs trigger their own CI) — it does not fall back to GITHUB_TOKEN. The 9 sibling repos rely on these secrets being available org-wide, but I could not verify that blog_example has access (secret listing is admin-gated). Please confirm blog_example is in the scope of the org APP_ID / APP_PRIVATE_KEY secrets before relying on the first backport. This is not a regression risk: the current action is already broken, so the migration is neutral-or-better either way.

Reference style

Uses @main, matching the open migration PRs (TYPO3-Documentation/TYPO3CMS-Tutorial-Editors#258, TYPO3-Documentation/render-guides#1196) and the recommendation in ADR-003 (TYPO3-Documentation/.github#6). If maintainers decide on SHA-pinning there, this can be pinned to match.

Related

• Tracked in [TASK] Migrate remaining repos to shared reusable workflows .github#5 (this was the last unchecked backport migration).

Test plan

• actionlint clean
• Maintainer confirms APP_ID/APP_PRIVATE_KEY reach blog_example
• First labeled+merged PR produces a backport PR (end-to-end)