Stop preview cleanup from deleting other PRs' previews (#4626)

`aws s3 rm` matches by key prefix, so the cleanup for PR 461 also removed the previews for PRs 4610 to 4619. A trailing slash limits the delete to the closed PR's own folder.

Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com>

Author: akira28

.github/workflows/preview-cleanup.yml

@@ -66,4 +66,5 @@ jobs:
           PR_NUMBER: ${{ github.event.pull_request.number }}
           S3_FOLDER: ${{ inputs.s3-folder }}
         run: |
-          aws s3 rm "s3://elastic-docs-v3-website-preview/${GITHUB_REPOSITORY}/${S3_FOLDER}/${PR_NUMBER}" --recursive
+          # The trailing slash matters: `s3 rm` matches by key prefix, so without it PR 461 also deletes 4610-4619.
+          aws s3 rm "s3://elastic-docs-v3-website-preview/${GITHUB_REPOSITORY}/${S3_FOLDER}/${PR_NUMBER}/" --recursive