Adds Ruby 3.2 to the CI matrix

[petergoldstein]

Also updates the checkout action to v3.

Getting tests to run green on Ruby 3.2 required an update to the fake_certificate_chain_validation_time method, such that it separated out positional and keyword arguments and only passed the keyword arguments to the wrapped method. Ruby 3.2 is somewhat more strict on the distinction between positional and keyword arguments.

This runs green on my fork.

[bdewater]

Thank you!