Upgrade Ruby version

[briri]

Upgrade Ruby from 2.6.3 to 2.7 or 3.x

See the release notes at: https://www.ruby-lang.org/en/

Related to #3103

[briri]

The big question here is whether or not we should consider upgrading to 3.0 or 3.1.

[benjaminfaure]

Seems like Rails 5 is not compatible with Ruby 2.7 according to these sources :
https://www.fastruby.io/blog/ruby/rails/versions/compatibility-table.html
rails/rails#38426

The official guide says 2.2.2 or newer : https://guides.rubyonrails.org/upgrading_ruby_on_rails.html

I tried switching from Ruby 2.6 to 2.7 on the roadmap code, basic features seems to be working fine, but I guess we can expect some side effects

[briri]

I just encountered a Brakeman warning that Ruby 2.7 EOL if June 2022

[benjaminfaure]

According to the Ruby website, 2.7 is still maintained (2.7.6 was released in April of this year)
https://www.ruby-lang.org/en/downloads/branches/
https://www.ruby-lang.org/en/news/2022/04/12/ruby-2-7-6-released/

Rails 5.2 is not compatible with Ruby 2.7 but Rails 6 is : rails/rails#38426

I suggest that we update to Rails 6 (see #3103) before upgrading to Ruby 3 as Rails 6.1 is compatible.

Plus we wouldn't have to upgrade Ruby when moving to Rails 7

[briri]

Upgraded to 2.7. Will open a new ticket for 3.0