reset Event System in TestRequest

To better simulate requests, event registration should be redone on each
simulated request.

_test/core/TestRequest.php

@@ -4,6 +4,7 @@
  * runtime inspection.
  */
 
+use dokuwiki\Extension\EventHandler;
 use dokuwiki\Input\Input;
 
 /**
@@ -148,6 +149,10 @@ class TestRequest {
         $_POST = $this->post;
         $_REQUEST = array_merge($_GET, $_POST);
 
+        // reset event handler
+        global $EVENT_HANDLER;
+        $EVENT_HANDLER = new EventHandler();
+
         // reset output buffer
         $this->output_buffer = '';