CI: Include Ruby 3.1

[olleolleolle]

MiniTest has released. https://rubygems.org/gems/minitest/versions/5.15.0 Any Ruby < 4.0.

This PR adds back head and Ruby 3.1.

[dhh]

3,1 seems to be failing.

[olleolleolle]

Looks a bit like a Gemfile can solve this:

Fetching gem metadata from https://rubygems.org/..........
  nokogiri-1.12.5-x86_64-linux requires ruby version < 3.1.dev, >= 2.5, which is
  incompatible with the current version, ruby 3.1.1p18
  Took   2.70 seconds

[olleolleolle]

@dhh I guess this small Gemfile.lock update does the trick.

[dhh]

Now the failure is something else.

[olleolleolle]

Alright! ruby-head is just not going to work yet.

nokogiri-1.13.3-x86_64-linux requires ruby version < 3.2.dev, >= 2.6, which is
incompatible with the current version, ruby 3.2.0p-1

[dhh]

"3 successful and 1 failing checks", isn't head supposed to just warn rather than block?

[olleolleolle]

@dhh I have unsuccessfully looked for an "allow failures" analogue in GH Actions.

[dhh]

If not, maybe just remove head for now 👍

[olleolleolle]

@dhh Perhaps this can be squashed on merge?