[Security] Add back ROLE_PREVIOUS_ADMIN to impersonated user

Author: chalasr

Firewall/SwitchUserListener.php

@@ -149,7 +149,7 @@ private function attemptSwitchUser(Request $request, string $username): ?TokenIn
         $this->userChecker->checkPostAuth($user);
 
         $roles = $user->getRoles();
-
+        $roles[] = 'ROLE_PREVIOUS_ADMIN';
         $token = new SwitchUserToken($user, $user->getPassword(), $this->providerKey, $roles, $token);
 
         if (null !== $this->dispatcher) {