Don't try to set invalid cookies.

In Rack 3.1, using invalid cookie keys was deprecated and in Rack 3.2,
using an invalid cookie key will raise an exception.

Escaping cookie keys is non-standard behaviour and is not understood by
clients, e.g. `document.cookies` will contain escaped keys. It also
doesn't round-trip correctly, as in, setting a header with a given name
won't have the same name in subsequent requests. In addition, the
escaping / unescaping behaviour in previous versions of Rack
[caused a security issue](GHSA-j6w9-fv6q-3q52).

Author: ioquatix

actionpack/test/dispatch/cookies_test.rb

@@ -115,11 +115,6 @@ def authenticate
       head :ok
     end
 
-    def set_with_with_escapable_characters
-      cookies["that & guy"] = "foo & bar => baz"
-      head :ok
-    end
-
     def authenticate_for_fourteen_days
       cookies["user_name"] = { "value" => "david", "expires" => Time.utc(2005, 10, 10, 5) }
       head :ok
@@ -493,12 +488,6 @@ def test_setting_the_same_value_to_permanent_cookie
     assert_equal({ "user_name" => "Jamie" }, response.cookies)
   end
 
-  def test_setting_with_escapable_characters
-    get :set_with_with_escapable_characters
-    assert_set_cookie_header "that+%26+guy=foo+%26+bar+%3D%3E+baz; path=/; SameSite=Lax"
-    assert_equal({ "that & guy" => "foo & bar => baz" }, @response.cookies)
-  end
-
   def test_setting_cookie_for_fourteen_days
     get :authenticate_for_fourteen_days
     assert_set_cookie_header "user_name=david; path=/; expires=Mon, 10 Oct 2005 05:00:00 GMT; SameSite=Lax"