chore: Add Ruby 3.2 to the CI matrix

[ydah]

Follow up: rspec/rspec-rails#2648

[pirj]

Thank you. There's a build failure related to mutex behaviour change that makes all 3.2 builds red. Usually, we change build and some doc files in a batch in a centralized way from https://github.com/rspec/rspec-dev/ to keep them in sync.