Drop support for EOL versions & test against newer ones

[sambostock]

The most important changes made in this PR are that it drops support for the following:

• Ruby < 2.6
  Note than 2.6 EOL is scheduled for 31 Mar 2022
  • 2.5 EOL was 31 Mar 2021
  • 2.4 EOL was 31 Mar 2020
• Active Support < 5.2
  • 5.1 EOL was 25 Aug 2019
  • 5.2 EOL was 09 Apr 2018
  • 4.2 EOL was 27 Apr 2017

Several related changes are made:

• We now also test against Ruby 3.0 & 3.1
• We now also test against Active Support 6.1, 7.0, & edge (rails/rail:main)
• Multiple gemfiles and gemspec are cleaned up
• All development dependencies are updated

[sambostock]

This failure seems to occur on only the Active Support 7.0 CI runs, but be fixed in the edge runs.

...activesupport-7.0.2.2/lib/active_support/xml_mini.rb:184:in `current_thread_backend':
   uninitialized constant ActiveSupport::XmlMini::IsolatedExecutionState (NameError)

        IsolatedExecutionState[:xml_mini_backend]

Using git bisect on rails/rails, I've identified rails/rails#44340 as fixing it. However, that PR mentions

For better or worse, this change will incidentally fix the instances of people requiring some individual files from Active Support without first loading active_support.rb that, while not officially supported, were previously working and recently started failing. (rails/rails#43851 rails/rails#43852 rails/rails#43889 rails/rails#43908 rails/rails#44336) This is not a reversal of that supported-usage policy, and a future change could re-break it at any time.

Based on that, we must have a usage of an Active Support internal file without require "active_support" first. It would probably make sense to track it down and address it before merging this, rather than skipping the 7.0 entries in the test matrix, but that is always an option. Note that (as far as I can tell), this is revealing an existing bug, not introducing one (though I may be wrong).

[sambostock]

The issue is that #50 added

deprecation_toolkit/lib/deprecation_toolkit.rb

Line 38 in 0bfe378

require "active_support"

near the bottom of the file, whereas if needs to be the first thing we do, before even

deprecation_toolkit/lib/deprecation_toolkit.rb

Line 3 in 0bfe378

load("tasks/ci_recorder.rake")

because the task code includes

deprecation_toolkit/lib/tasks/ci_recorder.rake

Line 5 in 0bfe378

require "active_support/core_ext/hash"

and as described in my previous comment, requiring pieces of Active Support before requiring the main file first is unsupported behaviour.

[rochlefebvre]

Nice update and nice cleanup! I learned a few tricks for managing several versioned gemfiles.

[sambostock]

I've only documented the user facing changes. Excluded are:

• the changes to CI infrastructure
• the changes to development dependency versions and config