Add SONAR_TOKEN to dependabot secrets

Currently GitHub build actions fails for dependabot (see here) with following error message:

Error: Failed to execute goal org.sonarsource.scanner.maven:sonar-maven-plugin:3.9.0.2155:sonar (default-cli) on project hogajama: You're not authorized to run analysis. No sonar.login or SONAR_TOKEN env variable was set -> [Help 1]

Tasks

• Add SONAR_TOKEN to dependabot secrets as it is in actions secrets