Add 3.1 and 3.2 to the list of Ruby CI versions

[igor-drozdov]

@mislav thanks for the approval! Can it be merged now or anything else needs to be done?

[mislav]

Sorry, I approved it out of habit, but I forgot that I cannot actually merge this because I don't work for GitHub anymore since recently and thus don't maintain this project. Maybe someone else will come around to this 🤞

[igor-drozdov]

@mislav ah, got it, thanks for the answer!