Bump codecov/codecov-action from 3 to 4 (#683)

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]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/unittests.yml

@@ -77,7 +77,7 @@ jobs:
           pytest -v --color yes -n auto --cov libpysal --cov-append --cov-report term-missing --cov-report xml .
 
       - name: Codecov
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
 
       - name: Generate and publish the report
         if: |