Add schema declaration to phpunit files. Remove parameters set to phpunit defaults.

Author: Steveb-p

phpunit.xml.dist

@@ -1,15 +1,11 @@
 <?xml version="1.0" encoding="UTF-8"?>
 
-<phpunit backupGlobals="false"
-         backupStaticAttributes="false"
-         colors="true"
-         convertErrorsToExceptions="true"
-         convertNoticesToExceptions="true"
-         convertWarningsToExceptions="true"
-         processIsolation="false"
-         stopOnFailure="false"
-         bootstrap="./vendor/autoload.php"
-        >
+<phpunit
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/7.5/phpunit.xsd"
+    colors="true"
+    bootstrap="./vendor/autoload.php"
+>
 
     <testsuites>
         <testsuite name="Symfony Async Event Dispatcher Test Suite">