Update codecov/codecov-action action to v6 (#770)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/ci.yml

@@ -129,7 +129,7 @@ jobs:
           PYTHONDEVMODE=1 pytest -v -ra --cov=murfey --cov-report=xml --cov-branch
 
       - name: Upload test results to Codecov
-        uses: codecov/codecov-action@v5
+        uses: codecov/codecov-action@v6
         with:
           name: ${{ matrix.python-version }}
           files: coverage.xml