Update activesupport requirement to allow 8.0

[coord-e]

This PR updates Active Support requirement of promenade to allow Rails 8.0. In my understanding, the main use of Active Support in promenade is the subscribers, and I don’t see anything interesting related to ActiveSupport::Subscriber and notifications in the 8.0 changelogs. https://github.com/rails/rails/blob/8-0-stable/activesupport/CHANGELOG.md

This PR also removes Ruby 3.1 (which is already EOL) from CI matrix.

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 100.00%. Comparing base (6cfd879) to head (edd080f). :warning: Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master       #78   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           38        38           
  Lines          856       856           
=========================================
  Hits           856       856           

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[coord-e]

@errm Could you check this, please? (no rush.)