Fix codecov action usage.

Author: davidlehn

.github/workflows/main.yaml

@@ -58,6 +58,6 @@ jobs:
     - name: Upload coverage to Codecov
       uses: codecov/codecov-action@v5
       with:
-        file: ./coverage/lcov.info
+        files: ./coverage/lcov.info
         fail_ci_if_error: true
         token: ${{ secrets.CODECOV_TOKEN }}