Fix env var expansion in sonar scanner args

The 'with:' block needs ${{ env.VAR }} syntax, not shell ${VAR}.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ToreMerkely

.github/workflows/sonar-pr-trigger.yml

@@ -67,8 +67,8 @@ jobs:
         uses: SonarSource/sonarqube-scan-action@v6.0.0
         with:
           args: >
-            -Dsonar.pullrequest.key=${PR_NUMBER}
-            -Dsonar.pullrequest.branch=${BRANCH}
+            -Dsonar.pullrequest.key=${{ env.PR_NUMBER }}
+            -Dsonar.pullrequest.branch=${{ env.BRANCH }}
             -Dsonar.pullrequest.base=main
 
       - name: Write scan summary