Fix style for rescue responses doc [ci skip]

 * Change 'Any ***s that are...' to 'Any *** that is...'
 * Fix style for default rescue_responses setting

This is a follow-up commit to:

 * https://github.com/rails/rails/pull/17076
 * https://github.com/yuki24/rails/commit/89b8836f2470c689f6b7d52cab3a418bb63aef26
Merge pull request #17153 from yuki24/fix-doc-format-for-rescue-responses

[Railsguides] Fix style for rescue responses doc [ci skip]