Update CI.yml

Author: stertooy

.github/workflows/CI.yml

@@ -70,3 +70,18 @@ jobs:
           name: "Manual"
           path: ./doc/manual.pdf
           if-no-files-found: error
+
+  citation:
+    name: "Validate citation"
+    runs-on: ubuntu-latest
+    if: github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name != github.event.pull_request.base.repo.full_name 
+
+    steps:
+
+      - name: "Checkout"
+        uses: actions/checkout@v4
+
+      - name: "Validate citation"
+        uses: dieghernan/cff-validator@v3
+        with:
+          install-r: true