ci: run unittest on matrix of os and python versions

.github/workflows/unittest.yml

@@ -7,20 +7,26 @@ on:
   pull_request:
   workflow_dispatch:
 
+defaults:
+  run:
+    shell: bash {0}
+
 jobs:
-  build:
-    runs-on: ubuntu-latest
+  test:
+    runs-on: ${{ matrix.os }}-latest
     strategy:
       fail-fast: false
       matrix:
-        python-version: [3.7, 3.8, 3.9]
+        os: [ubuntu, macos, windows]
+        python: [3.7, 3.9]
 
     steps:
       - uses: actions/checkout@v2
-      - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v2
+      - name: Set up Python
+        uses: actions/setup-python@v4
         with:
-          python-version: ${{ matrix.python-version }}
+          python-version: ${{ matrix.python }}
+          cache: "pip"
       - name: Install
         run: pip install ".[dev]"
       - name: test