Bump codecov/codecov-action from 2.1.0 to 3.1.0 (#61)

Bumps [codecov/codecov-action](https://github.com/codecov/codecov-action) from 2.1.0 to 3.1.0.
- [Release notes](https://github.com/codecov/codecov-action/releases)
- [Changelog](https://github.com/codecov/codecov-action/blob/master/CHANGELOG.md)
- [Commits](codecov/codecov-action@v2.1.0...v3.1.0)

---
updated-dependencies:
- dependency-name: codecov/codecov-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Wei Ji <[email protected]>

Author: dependabot[bot]

.github/workflows/main.yaml

@@ -36,7 +36,7 @@ jobs:
         run: |
           py.test --verbose --cov=. --cov-report=xml
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v2.1.0
+        uses: codecov/codecov-action@v3.1.0
         if: ${{ matrix.python-version }} == 3.9
         with:
           file: ./coverage.xml