Fix `CustomCops/AssertNot` to allow it to have failure message

Follow up of #32605.

1 files changed, 2 insertions, 2 deletions

diff --git a/actionpack/test/dispatch/response_test.rb b/actionpack/test/dispatch/response_test.rb
index 6d87314e97..0f37d074af 100644
--- a/actionpack/test/dispatch/response_test.rb
+++ b/actionpack/test/dispatch/response_test.rb
@@ -158,7 +158,7 @@ class ResponseTest < ActiveSupport::TestCase
       @response.status = c.to_s
       @response.set_header "Content-Length", "0"
       _, headers, _ = @response.to_a
-      assert !headers.has_key?("Content-Length"), "#{c} must not have a Content-Length header field"
+      assert_not headers.has_key?("Content-Length"), "#{c} must not have a Content-Length header field"
     end
   end
 
@@ -177,7 +177,7 @@ class ResponseTest < ActiveSupport::TestCase
       @response = ActionDispatch::Response.new
       @response.status = c.to_s
       _, headers, _ = @response.to_a
-      assert !headers.has_key?("Content-Type"), "#{c} should not have Content-Type header"
+      assert_not headers.has_key?("Content-Type"), "#{c} should not have Content-Type header"
     end
 
     [200, 302, 404, 500].each do |c|