Avoid running SonarCloud scan on pull requests.

Pull requests do not have access to the Sonar token, so always fail.

.github/workflows/tests.yml

@@ -28,6 +28,7 @@ jobs:
         run: git fetch --no-tags https://$GITHUB_ACTOR:${{ secrets.GITHUB_TOKEN }}@github.com/$GITHUB_REPOSITORY +refs/heads/main:refs/remotes/origin/main
       - name: SonarCloud scan
         uses: sonarsource/sonarcloud-github-action@master
+        if: ${{ github.event.type == 'push' }}
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           SONAR_TOKEN: ${{ secrets.SONAR_TOKEN }}