Use for test job a macOS machine to be able to run golden tests (#220)

#138 & #216 are adding golden tests. Golden tests can only run on one platform. We decided to pick macOS as the platform because primary using macOS. Therefore, should our CI use macOS machines. Otherwise, the Golden Tests are skipped.

.github/workflows/main.yml

@@ -59,7 +59,7 @@ jobs:
       - run: addlicense -check -c "Sharezone UG (haftungsbeschränkt)" -f header_template.txt -ignore "**/GeneratedPluginRegistrant.swift" . 
 
   test:
-    runs-on: ubuntu-latest
+    runs-on: macos-latest
     steps:
       - uses: actions/checkout@v2
 
@@ -75,7 +75,7 @@ jobs:
         run: pub global activate --source path "$CI_CD_DART_SCRIPTS_PACKAGE_PATH"
 
       # So we can just use "sz COMMAND" instead of "dart ../path/to/script.dart ..."
-      - run: echo $(realpath ./bin) >> $GITHUB_PATH
+      - run: echo $(pwd)/bin >> $GITHUB_PATH
 
       - name: Run tests via "sz test"
         run: sz test -v