Remove version checks against `ruby < 2.7`

[thdaraujo]

We want to drop support for EOL Ruby versions.

Tasks

• [ ] Remove version checks here and here.
• [ ] Update Targeted Ruby Version for Rubocop.
• [ ] Update spec.required_ruby_version = '>= 2.5' to spec.required_ruby_version = '>= 2.7'

See https://github.com/faker-ruby/faker/issues/2522 for more details.