[TASK] Upgrade the Ruby version to Ruby 3.1

[arielj]

Description:

The app is currently running on Ruby 3.0. We want to upgrade to Ruby 3.1 to be able to use the Heroku-22 stack (Ruby 3.0 is only supported in Heroku-18 and Heroku-20 stacks).

Resources:

https://devcenter.heroku.com/articles/ruby-support#ruby-versions
https://www.fastruby.io/blog/heroku/upgrades/Heroku-22-Stack-Upgrade-Guide.html

I will abide by the [code of conduct] (https://github.com/fastruby/benchmark.fyi/blob/main/CODE_OF_CONDUCT.md)