CI: attempt to fix code coverage upload

Author: ctrueden

.github/workflows/build.yml

@@ -60,5 +60,5 @@ jobs:
         bin/lint.sh
 
     - name: Upload coverage
-      if: matrix.platform == 'ubuntu-latest' && matrix.python-version == '3.13' && matrix.java-version == '11'
+      if: matrix.os == 'ubuntu-latest' && matrix.python-version == '3.13' && matrix.java-version == '11'
       uses: codecov/codecov-action@v4