ci(github-actions): replace deprecated file key with files in codecov-action

Author: Lee-W

.github/workflows/pythonpackage.yml

@@ -33,6 +33,6 @@ jobs:
         uses: codecov/codecov-action@v5
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
-          file: ./coverage.xml
+          files: ./coverage.xml
           flags: unittests
           name: codecov-umbrella