Remove macOS from CI build matrix in GitHub Actions workflow

Author: stefanhahmann

.github/workflows/build.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ ubuntu-latest, macos-latest ]
+        os: [ ubuntu-latest ]
     steps:
       - uses: actions/checkout@v2
       - name: Set up Java