enabled build matrix back

Author: antelle

.github/workflows/ci-checks.yaml

@@ -9,8 +9,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest]
-#        os: [macos-latest, windows-latest, ubuntu-latest]
+        os: [macos-latest, windows-latest, ubuntu-latest]
     steps:
       - name: Checkout
         uses: actions/checkout@v2