docs: fix indentation

Author: kenjis

mkdocs.yml

@@ -53,7 +53,7 @@ nav:
     - Testing: testing.md
     - session_auth_event_and_logging.md
   - Customization:
-      - customization.md
+    - customization.md
   - Guides:
     - guides/forcing_password_reset.md
     - guides/banning_users.md