revert to use local phpunit.xsd

Author: pascalheidmann

phpunit.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-	xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.5/phpunit.xsd"
+	xsi:noNamespaceSchemaLocation="tests/phpunit.xsd"
 	bootstrap="tests/bootstrap-runtime-reflection.php"
 	cacheResult="false"
 	colors="true"