GitHub-Actions: Only run SonarCloud when token is set

Pull Requests often don't have the token (e.g. somebody outside of Songoda created it)

.github/workflows/sonarcloud.yml

@@ -10,21 +10,26 @@ jobs:
   build:
     name: Build
     runs-on: ubuntu-latest
+    env:
+      SONAR_TOKEN: ${{ secrets.SONAR_TOKEN }}
     steps:
       # Setup Java
       - uses: actions/setup-java@v2
+        if: ${{ env.SONAR_TOKEN != null }}
         with:
           java-version: 17
           distribution: adopt
 
       # Checkout project files
       - uses: actions/checkout@v2
+        if: ${{ env.SONAR_TOKEN != null }}
         with:
           fetch-depth: 0  # Shallow clones should be disabled for a better relevancy of analysis
 
       # Caches
       - name: 'Cache: Maven'
         uses: actions/cache@v2
+        if: ${{ env.SONAR_TOKEN != null }}
         with:
           path: ~/.m2/repository
           key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
@@ -36,7 +41,7 @@ jobs:
           key: ${{ runner.os }}-sonar
 
       - name: Analyze project
+        if: ${{ env.SONAR_TOKEN != null }}
         run: mvn -B verify org.sonarsource.scanner.maven:sonar-maven-plugin:sonar -Dsonar.projectKey=songoda_SongodaCore
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}  # Needed to get PR information, if any
-          SONAR_TOKEN: ${{ secrets.SONAR_TOKEN }}