Issue #3590975: Use \Drupal::currentUser()->setAccount() in simplesamlphp_auth_user_logout()

Summary

Fixes a fatal error during logout for SAML-authenticated users when simplesamlphp_auth_user_logout() calls setAccount() on the hook_user_logout argument instead of the current user proxy.

Closes #3590975

Problem

When SAML logout handling runs (isActivated() and isAuthenticated()), the module executes:

$account->setAccount(new AnonymousUserSession());