Also, edge rails requires ruby 3.2 now, so it's dropped from ruby 3.1.

Add rails 7.2 and 8.0 to the build matrix

- Add Rails 8.1
- Add Ruby 3.4
- Run Ruby head against Rails 8.1
- Fix missing `logger` require in Rails < 7
- Add require for `bigdecimal` and `mutex_m` in Ruby 3.4+

Given `ActiveSupport::Configurable` is deprecated without replacement
and will be removed in Rails 8.2, we can stop using it in Rails 8.1+
and instead create methods that delegate to
`ActionController::Base.config` instead.

Fixes #23, closes #24

Co-authored-by: Scott Klein <scott@klein.io>

Reference:
- https://github.com/omniauth/omniauth/releases/tag/v2.0.0
- #24 (comment)
- omniauth/omniauth#1075

* Stop using deprecated `ActiveSupport::Configurable` when this gem is
  running against Action Pack version 8.1 and later (#23, #24)