Mark User::eraseCredentials as deprecated

This avoids the deprecation warning of Symfony about the deprecation of
the method. Our User class already excludes the plain password from the
serialized data even when this method is not called.

Author: stof

src/Model/User.php

@@ -183,6 +183,7 @@ public function addRole($role)
         return $this;
     }
 
+    #[\Deprecated]
     public function eraseCredentials(): void
     {
         $this->plainPassword = null;