ci: fix code coverage

Author: josantonius

.github/workflows/ci.yml

@@ -89,7 +89,7 @@ jobs:
 
       - name: 'Run code coverage'
         run: |
-          vendor/bin/phpunit --coverage-html coverage
+          vendor/bin/phpunit --coverage-clover=coverage.xml
 
       - name: Send code coverage report to Codecov.io
         uses: codecov/codecov-action@v2