Add `ruby2_keywords` for argument forwarding.

[ioquatix]

The lemon gem needs an update to support Ruby 3.x - without it I can't update the tests for facets.

You need to add ruby2_keywords to the argument forwarding:

https://github.com/rubyworks/lemon/blob/master/lib/lemon/test_method.rb#L86-L89

Otherwise keyword arguments won't be forwarded correctly.