github/workflows: Bump codecov/codecov-action from 5 to 6.

Bumps [codecov/codecov-action](https://github.com/codecov/codecov-action) from 5 to 6.
- [Release notes](https://github.com/codecov/codecov-action/releases)
- [Changelog](https://github.com/codecov/codecov-action/blob/main/CHANGELOG.md)
- [Commits](codecov/codecov-action@v5...v6)

---
updated-dependencies:
- dependency-name: codecov/codecov-action
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/ports_unix.yml

@@ -93,7 +93,7 @@ jobs:
         (cd ports/unix && gcov -o build-coverage/py ../../py/*.c || true)
         (cd ports/unix && gcov -o build-coverage/extmod ../../extmod/*.c || true)
     - name: Upload coverage to Codecov
-      uses: codecov/codecov-action@v5
+      uses: codecov/codecov-action@v6
       with:
         # Only fail the job on error if a token is set, or we're running against upstream repo.
         # This avoids the annoying situation of the job failing on every push to a fork (if no token is set).