Merge pull request #115 from nils-a/feature/GH-114

(#114) build PR only if they originate in remote repos

.github/workflows/build.yml

@@ -9,6 +9,7 @@ on:
 jobs:
   build:
     runs-on: ${{ matrix.os }}
+    if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
     strategy:
       matrix:
         os: [windows-2022, ubuntu-22.04, macos-12]