Fix mutation testing

Author: staabm

.github/workflows/tests.yml

@@ -307,7 +307,7 @@ jobs:
         run: |
           php -d pcov.enabled=1 tests/vendor/bin/paratest \
             --passthru-php="'-d' 'pcov.enabled=1'" \
-            --coverage-xml=tmp/coverage/coverage-xml --log-junit=tmp/coverage/junit.xml
+            --coverage-xml=tmp/coverage/coverage-xml --log-junit=tmp/coverage/junit.xml \
             --exclude-source-from-xml-coverage
 
       - name: "Run infection"