Update codecov action to handle different OS and Python versions (#1254)

codecov/codecov-action#80 (comment)

Author: leezu

.github/workflows/unittests.yml

@@ -41,6 +41,6 @@ jobs:
         run: |
           python -m pytest --cov=./ --cov-report=xml --durations=50 tests/
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v1
+        uses: codecov/codecov-action@v1.0.10
         with:
           env_vars: OS,PYTHON