Update CSSUoB/pr-auto-updater action to v2.2.1 (#536)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/pr-auto-updater.yaml

@@ -10,7 +10,7 @@ jobs:
             pull-requests: write
             contents: write
         steps:
-            - uses: CSSUoB/pr-auto-updater@v2.1.2
+            - uses: CSSUoB/pr-auto-updater@v2.2.1
               env:
                 GITHUB_TOKEN: '${{ secrets.PR_AUTO_UPDATE_TOKEN }}'
                 PR_FILTER: 'labelled'