All of our tests were testing the `ActionController::Live` behavior in a
standalone environment, without going through the router or behaving
like a real application.

This resulted in `ActionController::Live` throwing the exception
`undefined method 'request' for #<ActionDispatch::Request:0x00000003ad1148>`
because `make_response!` was expecting a response instead of a request.

The expectation of a response came from `set_response!` in non-router
tests setting the response and passing it to `make_response!`. In the
case of an application we would hit `serve` in `RouteSet` first which
would send us to `make_response!` with a request sent instead of a
response.

The changes here remove `set_response!` so `make_response!` always
receives a request.

Thanks to KalabiYau for help with the investigation and solution.

Fixes #22524

[Eileen M. Uchitelle & KalabiYau]