Bump codecov/codecov-action from 3 to 4 (FluxML#2376)

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/ci.yml

@@ -56,7 +56,7 @@ jobs:
         if: contains(fromJson('["1", "1.9"]'), matrix.version) && matrix.os == 'ubuntu-latest'
       - uses: julia-actions/julia-processcoverage@v1
         if: contains(fromJson('["1", "1.9"]'), matrix.version) && matrix.os == 'ubuntu-latest'
-      - uses: codecov/codecov-action@v3
+      - uses: codecov/codecov-action@v4
         if: contains(fromJson('["1", "1.9"]'), matrix.version) && matrix.os == 'ubuntu-latest'
         with:
           file: lcov.info