[x] Update default development ruby from 2.7.5 to 3.1.6
Why?
This is the ruby version we use most often when editing & changing the gem, we should ensure this is a supported version of ruby for security updates at least. Currently 3.1.6 is the oldest ruby version receiving security updates, so let's pin to that. (We don't want to default to the latest & greatest, because we often can't make use of new ruby features due to the gem having to work on 1.9.3)
What?
Why?
This is the ruby version we use most often when editing & changing the gem, we should ensure this is a supported version of ruby for security updates at least. Currently 3.1.6 is the oldest ruby version receiving security updates, so let's pin to that. (We don't want to default to the latest & greatest, because we often can't make use of new ruby features due to the gem having to work on 1.9.3)