Run pyright on matrix of platforms and python versions (#5072)

* Run pyright on matrix of platforms and python versions

* Drop 3.10 from matrix, as it fails

.github/workflows/tests.yml

@@ -88,13 +88,18 @@ jobs:
   pyright:
     name: Run pyright against the stubs
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-platform: ["Linux", "Windows", "Darwin"]
+        python-version: [3.6, 3.7, 3.8, 3.9]
+      fail-fast: false
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
       - uses: actions/setup-node@v2
         with:
           node-version: '14'
-      - run: ./tests/pyright_test.py
+      - run: ./tests/pyright_test.py --pythonplatform ${{ matrix.python-platform }} --pythonversion ${{ matrix.python-version }}
 
   stubtest:
     name: Check stdlib with stubtest