Build(deps): Bump codecov/codecov-action from 3.1.4 to 4.0.0

Bumps [codecov/codecov-action](https://github.com/codecov/codecov-action) from 3.1.4 to 4.0.0.
- [Release notes](https://github.com/codecov/codecov-action/releases)
- [Changelog](https://github.com/codecov/codecov-action/blob/main/CHANGELOG.md)
- [Commits](codecov/codecov-action@v3.1.4...v4.0.0)

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

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

.github/workflows/tests.yml

@@ -65,7 +65,7 @@ jobs:
     # Only upload to codecov on pull requests so that we don't trigger rate limit blocks
     - name: Upload to Codecov
       if: matrix.os == 'ubuntu-latest' && matrix.python-version == 3.9 && matrix.sphinx == '~=7.0' && github.repository == 'executablebooks/sphinx-book-theme' && github.event_name == 'pull_request'
-      uses: codecov/codecov-action@v3.1.4
+      uses: codecov/codecov-action@v4.0.0
       with:
         name: ebp-sbt-pytests-py3.7
         flags: pytests