add a GitHub workflow to validate if commits are signed on PRs

.github/workflows/check-signed.yml

@@ -0,0 +1,14 @@
+---
+name: Validate if commits are signed
+on: [pull_request, pull_request_target]
+
+jobs:
+  signed-commits-check:
+    runs-on: ubuntu-latest
+    steps:
+
+      - name: Check out the repository code
+        uses: actions/checkout@v4.1.4
+
+      - name: Check if the commits are signed
+        uses: 1Password/check-signed-commits-action@v1