Throw error if sonar label is missing

.github/workflows/sonar-scan.yml

@@ -9,9 +9,12 @@ env:
 
 jobs:
   sonar:
-    if: contains(github.event.pull_request.labels.*.name, 'sonar-scan-approved')
     runs-on: ubuntu-latest
     steps:
+      - name: Check the presence of the label `sonar-scan-approved`
+        if: contains(github.event.pull_request.labels.*.name, 'sonar-scan-approved') != true
+        run: echo "Add the label 'sonar-scan-approved' to activate Sonar scan"; exit 1
+
       - uses: actions/checkout@v3
         name: Checkout ${{ env.HEAD_REPOSITORY }}:${{ env.HEAD_REF }}
         with: