Make PR preview cleanup idempotent

[ANonABento]

Problem

.github/workflows/pr-clean-up.yml assumes the preview folder exists and that deleting it always creates a commit:

rm -r './previews/pr-${{ github.event.pull_request.number }}'
git commit -am "Delete preview for PR #${{ github.event.pull_request.number }}"

If a PR never deployed a preview, the folder was already removed, or the folder path changes, rm -r fails. If there are no tracked changes after deletion, git commit -am fails. Either case can make the cleanup workflow report a failure even though there is nothing left to clean.

Suggested fix

• Use rm -rf or explicitly check whether the preview directory exists.
• Use git status --porcelain before committing and skip the commit/push when there are no changes.
• Consider using pinned SHAs for the unpinned actions/checkout@v3 step while touching the workflow.

Relevant file

• .github/workflows/pr-clean-up.yml