fix upper case self

Author: wo14580

tests/auth_plugin_test.php

@@ -1049,7 +1049,7 @@ public function test_user_logout_userkey_when_user_is_not_logged_in() {
 
         $this->expectException(moodle_exception::class);
         $this->expectExceptionMessage(
-            sprintf("Unsupported redirect to %s detected, execution terminated.", SELF::REDIRECTION_PATH)
+            sprintf("Unsupported redirect to %s detected, execution terminated.", self::REDIRECTION_PATH)
         );
 
         $this->auth->user_logout_userkey();