Fixes #23824: User data serialised multiple times on save when loaded via loadByUsername.

Unserialises the extra data when loading a user using the loadByUsername method of the User model.

Author: mustdobetter

app/code/Magento/User/Model/User.php

@@ -671,6 +671,10 @@ public function loadByUsername($username)
     {
         $data = $this->getResource()->loadByUsername($username);
         if ($data !== false) {
+            if (is_string($data['extra'])) {
+                $data['extra'] = $this->serializer->unserialize($data['extra']);
+            }
+
             $this->setData($data);
             $this->setOrigData();
         }