Remove 'Ruby' action now that there is a separate 'RSpec' and 'Rubocop'

[technicalpickles]

These two new actions were added in https://github.com/open-feature/ruby-sdk/pull/11 , but the Ruby step that runs Rake, which runs rubocop and rspec, is still around.

I noticed this because I was surprised by how many checks were running each commit:

Removing it would drop checks from 29 to 19.