Add a GitHub action to block until all depends-on are merged

.github/workflows/pr.yml

@@ -0,0 +1,23 @@
+---
+
+name: Pull Request
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+jobs:
+
+  check-all-dependencies-are-merged:
+    name: "Check all dependencies are merged"
+    runs-on: ubuntu-latest
+    steps:
+
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Check all dependent Pull Requests are merged
+        uses: depends-on/depends-on-action@main
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          check-unmerged-pr: true
+
+...