docs: add Project Files in upgrade_4211.rst

Author: kenjis

user_guide_src/source/installation/upgrade_4211.rst

@@ -69,4 +69,4 @@ many will be simple comments or formatting that have no effect on the runtime:
 * app/Config/Toolbar.php
 * app/Views/welcome_message.php
 * composer.json
-
+* phpunit.xml.dist