build: disable SonarCloud for fork pull requests

Author: westarle

.github/workflows/sonar.yaml

@@ -8,6 +8,7 @@ on:
 jobs:
   build:
     name: Build
+    if: github.event.pull_request.head.repo.full_name == github.repository || github.event_name != 'pull_request'
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v3