run sonar when merging pull requests into master

[xzel23]

sonar should also run when pull requests are merged.

@svanteschubert since I do not have access to the settings in Git, do you know if the configuration described in #386 has been done? We only need the secrets.SONAR_TOKEN and change the sonar credentials in Maven.yml:

      - name: Build and analyze
        env:
          SONAR_TOKEN: ${{ secrets.SONAR_TOKEN }}
        run: >
          mvn -B verify
          -Dsonar.host.url=https://sonarcloud.io
          -Dsonar.projectKey=<FILL IN>
          -Dsonar.organization=<FILL_IN>
          -Dsonar.coverage.jacoco.xmlReportPaths=target/site/jacoco-ut/jacoco.xml
          org.sonarsource.scanner.maven:sonar-maven-plugin:sonar

If you cannot change the settings and update the configuration, can you tell me who I should contact?