Fix `make_response!` when called by `serve` in `RouteSet`

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]

actionpack/lib/action_controller/metal/live.rb

@@ -36,8 +36,7 @@ module Live
     extend ActiveSupport::Concern
 
     module ClassMethods
-      def make_response!(response)
-        request = response.request
+      def make_response!(request)
         if request.get_header("HTTP_VERSION") == "HTTP/1.0"
           super
         else
@@ -287,9 +286,5 @@ def response_body=(body)
       super
       response.close if response
     end
-
-    def set_response!(response)
-      @_response = self.class.make_response! response
-    end
   end
 end

actionpack/test/controller/live_stream_test.rb

@@ -442,3 +442,42 @@ def test_nil_callback
     end
   end
 end
+
+class LiveStreamRouterTest < ActionDispatch::IntegrationTest
+  class TestController < ActionController::Base
+    include ActionController::Live
+
+    def index
+      response.headers['Content-Type'] = 'text/event-stream'
+      sse = SSE.new(response.stream)
+      sse.write("{\"name\":\"John\"}")
+      sse.write({ name: "Ryan" })
+    ensure
+      sse.close
+    end
+  end
+
+  def self.call(env)
+    routes.call(env)
+  end
+
+  def self.routes
+    @routes ||= ActionDispatch::Routing::RouteSet.new
+  end
+
+  routes.draw do
+    get '/test' => 'live_stream_router_test/test#index'
+  end
+
+  def app
+    self.class
+  end
+
+  test "streaming served through the router" do
+    get "/test"
+
+    assert_response :ok
+    assert_match(/data: {\"name\":\"John\"}/, response.body)
+    assert_match(/data: {\"name\":\"Ryan\"}/, response.body)
+  end
+end