Set XDEBUG_MODE to "coverage" when running tests

Author: dru1x

.github/workflows/test.yml

@@ -27,6 +27,8 @@ jobs:
           configuration: phpunit.xml.dist
           coverage_text: true
           coverage_clover: coverage.xml
+        env:
+          XDEBUG_MODE: coverage
 
       - name: Enforce coverage threshold
         if: matrix.php-version == '8.2'