Bump codecov/codecov-action from 3 to 4 (westpa#379)

* Bump codecov/codecov-action from 3 to 4

Bumps [codecov/codecov-action](https://github.com/codecov/codecov-action) from 3 to 4.
- [Release notes](https://github.com/codecov/codecov-action/releases)
- [Changelog](https://github.com/codecov/codecov-action/blob/main/CHANGELOG.md)
- [Commits](codecov/codecov-action@v3...v4)

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

Signed-off-by: dependabot[bot] <[email protected]>

* Update test.yaml

Add CODECOV_TOKEN for codecov-action@v4.

---------

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Jeremy M. G. Leung <[email protected]>

.github/workflows/test.yaml

@@ -76,12 +76,14 @@ jobs:
         pytest -v --cov=westpa --cov-report=xml --color=yes tests
 
     - name: CodeCov
-      uses: codecov/codecov-action@v3
+      uses: codecov/codecov-action@v4
       with:
         file: ./coverage.xml
         flags: unittests
         name: codecov-{{ '${{ matrix.os }}' }}-py{{ '${{ matrix.python-version }}' }}
         fail_ci_if_error: false
+      env:
+        CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
 
   install-dev:
     strategy: