ci(files-external): consolidate workflows

[susnux]

Summary

The idea is to only have one workflow to reduce total number of actions.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI

[SystemKeeper]

/backport! stable35

[SystemKeeper]

/backport! to stable35

[backportbot]

The backport to stable35 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable35
git pull origin stable35

# Create the new backport branch
git checkout -b backport/61222/stable35

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 003a64da

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/61222/stable35

Error: Failed to check for changes with origin/stable35: No changes found in backport branch

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[SystemKeeper]

Closing in favor of #63800