ci: 🎡 Add check for fast-forward merges

.github/workflows/main.yml

@@ -73,6 +73,7 @@ jobs:
     name: Building and releasing project
     runs-on: ubuntu-latest
     needs: [lint, build, test]
+    if: github.event_name == 'push'
     steps:
       - uses: actions/checkout@v3
         with:
@@ -112,4 +113,28 @@ jobs:
       - name: Clear SSH key
         run: |
           shred /tmp/id_ed25519
+  
+  check-fast-forward:
+    name: Check if fast forwarding is possible
+    runs-on: ubuntu-latest
+    needs: [lint, build, test]
+    if: github.event_name == 'pull_request'
+
+    permissions:
+      contents: read
+      # We appear to need write permission for both pull-requests and
+      # issues in order to post a comment to a pull request.
+      pull-requests: write
+      issues: write
+
+    steps:
+      - name: Checking if fast forwarding is possible
+        uses: sequoia-pgp/fast-forward@v1
+        with:
+          merge: false
+          # To reduce the workflow's verbosity, use 'on-error'
+          # to only post a comment when an error occurs, or 'never' to
+          # never post a comment.  (In all cases the information is
+          # still available in the step's summary.)
+          comment: never
 # TODO @polymath-eric: add SonarCloud step when the account confusion is sorted