set minimum Ruby version to 3.2+

[maxveldink]

With Ruby 3.4 soon to be released, we need to consider raising the minimum Ruby version for this project (and others) to Ruby 3.2+ at least (ideally Ruby 3.3 once 3.4 drops). This depends on the current Ruby versions of the integrations, so we'd need to be careful to update those as well.

What prompted this was that when I updated deps recently, some of them were dropping Ruby 3.0 support, which will make that process risky in the future. We'll want to get ahead of that.

[shawnpyle]

We are using this on 3.3.5 in development https://github.com/tithely/faithteams-api/blob/master/.tool-versions
but it does need to be upgraded here https://github.com/tithely/faithteams-api/blob/master/faithteams-api.gemspec#L15.