Switch feature branch builds to Ruby 3.1
Related to &10034 (closed). Once the Gem audit is complete and we have tackled all known issues, switch the feature branch builds to use Ruby 3.1. This means updating the NEXT_RUBY_VERSION
variable in CI config to 3.1. Ensure that the variables USE_NEXT_RUBY_VERSION_IN_NIGHTLY
and USE_NEXT_RUBY_VERSION_IN_AUTODEPLOY
are set to false in all the mirrors before this is done.
Edited by Balasankar 'Balu' C