Fix wrong kwarg "record" from #18872

PR #18772 changed the parameters of `stale?` to use `kwargs`.
[As for this comment](https://github.com/rails/rails/pull/18872/files#r24456288)
the default value for the `etag` parameter should be `record`, not `nil`.

This commit fixes the code and introduces a test that:

- passed before #18872
- fails on the current master (after #18772)
- passes again after setting the default value of `etag` to `record`.

1 files changed, 1 insertions, 1 deletions

diff --git a/actionpack/lib/action_controller/metal/conditional_get.rb b/actionpack/lib/action_controller/metal/conditional_get.rb
index bd7689a843..3a5929adef 100644
--- a/actionpack/lib/action_controller/metal/conditional_get.rb
+++ b/actionpack/lib/action_controller/metal/conditional_get.rb
@@ -155,7 +155,7 @@ module ActionController
     #     super if stale? @article, template: 'widgets/show'
     #   end
     #
-    def stale?(record = nil, etag: nil, last_modified: nil, public: nil, template: nil)
+    def stale?(record = nil, etag: record, last_modified: nil, public: nil, template: nil)
       fresh_when(record, etag: etag, last_modified: last_modified, public: public, template: template)
       !request.fresh?(response)
     end