Add workflow to delete PR cache

.github/workflows/cleanup.yaml

@@ -0,0 +1,33 @@
+---
+name: Cleanup
+
+on:
+  pull_request:
+    types:
+      - closed
+
+jobs:
+  cleanup-cache:
+    runs-on: ubuntu-latest
+    steps:
+      - name: 'Cleanup PR cache'
+        run: |
+          gh extension install actions/gh-actions-cache
+
+          REPO="${{ github.repository }}"
+          BRANCH="refs/pull/${{ github.event.pull_request.number }}/merge"
+
+          echo "Fetching list of cache key"
+          cacheKeysForPR=$(gh actions-cache list -R $REPO -B $BRANCH | cut -f 1 )
+
+          ## Setting this to not fail the workflow while deleting cache keys.
+          set +e
+          echo "Deleting caches..."
+          for cacheKey in $cacheKeysForPR
+          do
+            gh actions-cache delete $cacheKey -R $REPO -B $BRANCH --confirm
+          done
+          echo "Done"
+        shell: bash
+        env:
+          GH_TOKEN: ${{ github.token }}