Isolate changes for Ruby 3.1 w/out Rails 7

[petergoldstein]

This is not a cherry-pick, but it should give you the code changes required for the 5.1 maintenance branch to support Ruby 3.1 / Rails 6.1.

It's going to be really difficult to pull apart the parameter parsing in have_enqueued_mail.rb and I would recommend we not even try. Just put it all in the 5-1-maintenance branch.

[JonRowe]

It's going to be really difficult to pull apart the parameter parsing in have_enqueued_mail.rb and I would recommend we not even try. Just put it all in the 5-1-maintenance branch.

That's already done, I rewound main and repicked the relevant non rails 7 commits.

[petergoldstein]

@JonRowe Not as far as I can tell.

The Ruby 3.1 / Rails 6.1 fixes were built on top of the have_enqueued_matcher.rb fixes put in to get Rails 7 working - #2546

5-1-maintenance is broken with Ruby 3.1 / Rails 6.1. Splitting out the fixes for addressing that from those for Rails 7 will be messy, time consuming, and largely unnecessary.

[JonRowe]

I will close in favour of #2562 then, I will work out the fixes for the existing supported releases on 3.1 and leave you two to work on Rails 7 in main.