* Fix logout completion for SP

Reference parameters need to be explicitely marked as such in the arguments
array when using call_user_func_array().

Fixes the following exception:

SimpleSAML\Error\Exception: Warning - Parameter 1 to SimpleSAML\Auth\Source::completeLogout() expected to be a reference, value given at .../vendor/simplesamlphp/simplesamlphp/src/SimpleSAML/HTTP/RunnableResponse.php:72
Backtrace:
4 .../vendor/simplesamlphp/simplesamlphp/public/_include.php:86 (SimpleSAML_error_handler)
3 [builtin] (call_user_func_array)
2 .../vendor/simplesamlphp/simplesamlphp/src/SimpleSAML/HTTP/RunnableResponse.php:72 (SimpleSAML\HTTP\RunnableResponse::sendContent)
1 .../vendor/symfony/http-foundation/Response.php:394 (Symfony\Component\HttpFoundation\Response::send)
0 .../vendor/simplesamlphp/simplesamlphp/public/module.php:14 (N/A)

* Add note in changelog

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Co-authored-by: Tim van Dijen <tvdijen@gmail.com>