fix bug in BasicModel test

.github/workflows/build-and-test.yaml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: ubuntu-latest
+        os: [ubuntu-latest]
         python-version: [3.8, 3.9]
     steps:
     - uses: actions/checkout@v2