[11.x] Fix docblock for RoutingServiceProvider

[seriquynh]

The registerPsrRequest and registerPsrResponse methods of RoutingServiceProvider just register binding resolutions and don't actually throw exceptions.

In Laravel app, it only throws exceptions when someone calls ->make(Psr\Http\Message\ServerRequestInterface::class) or ->make(Psr\Http\Message\ResponseInterface::class) without installing the nyholm/psr7 package,