update ruby compatibility set
2.4 and 2.5 are EOL -> drop support for them 3.1 is newly released -> add support (no changes required)
minimal rubocop hints are now for 2.6
BUG: 450704
2.4 and 2.5 are EOL -> drop support for them 3.1 is newly released -> add support (no changes required)
minimal rubocop hints are now for 2.6
BUG: 450704