Delete caches associated with a branch after it has been merged into main

Author: RBusarow

.github/workflows/delete-pr-branch-caches.yml

@@ -0,0 +1,18 @@
+name: Delete Unused Caches
+
+on:
+  pull_request:
+    types: [ closed ]
+
+jobs:
+
+  # This deletes the caches created by the branch while it was in PR.
+  # Those caches are inaccessible to it once it's merged, so they can be deleted.
+  delete-orphaned-caches:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: snnaplab/delete-branch-cache-action@v1
+        with:
+          # Specify explicitly because the ref at the time of merging
+          # will be a branch name such as 'main', 'develop'
+          ref: refs/pull/${{ github.event.number }}/merge