Skip SonarQube analysis on PR from fork

[maruTA-bis5]

CI workflow on fork always failure.

Steps

1. Fork this repository.
2. Make some modification and commit it.
3. Open PR.
4. Approve running workflow by maintainer
   • CI for latest version is failing due to these error:

     Error:  Failed to execute goal org.sonarsource.scanner.maven:sonar-maven-plugin:3.9.1.2184:sonar (default-cli) on project mattermost4j-parent: Project not found. Please check the 'sonar.projectKey' and 'sonar.organization' properties, the 'SONAR_TOKEN' environment variable, or contact the project administrator -> [Help 1]