fix(ci): make coverage artifact name unique per Python version

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: vinnytherobot

.github/workflows/ci.yml

@@ -60,5 +60,5 @@ jobs:
       - name: Upload coverage artifact
         uses: actions/upload-artifact@v4
         with:
-          name: coverage-xml
+          name: coverage-xml-${{ matrix.python-version }}
           path: coverage.xml