[4.x] Fix response typehint in boot

[Jade-GG]

As it turns out, the Laravel RedirectResponse does not inherit the Laravel Response class. Instead, it extends the Symfony RedirectResponse which only inherits the Symfony Response class.

This means that we can't use the base Response class here. As the setPrivate function comes from the base Symfony class we can just use that instead. This sidesteps needing to define all the possible Response types we might get.