Add Minitest 6 Support

[rmm5t]

Note

Do not merge this until we have a new 2.4.7 or 2.5.0 release of guard-minitest to account for #165.

What does it do?

• Remove --guard flag for minitest 6 support (while maintaining minitest 5 support)
• Limit minitest dependency to v5 or v6 (removes support for minintest v3 and v4 and requires ruby >= 3.2)

What else do you need to know?

• Afterwards, the goal of this PR is to lead in a new 3.0.0 release of guard-minitest.

Related Issues

• GitHub actions #165

[rmm5t]

@thibaudgg @rymai What's the appetite for more help here to get guard-minitest up and running with Minitest 6?

In addition to this PR, it looks like the CI suite could use some help both porting to github actions and also modernizing the build matrix. I'm happy to help if we can get more eyes on this gem.

[thibaudgg]

Hey @rmm5t,

For full discloser, I haven't used guard and guard-minitest for quite a while now, so I'm a bit out of the loop. But please go ahead, I think it makes sense to first give the tests suite and CI a bit of love (even rewrite it all with minitest instead of RSpec) and then support minitest 6 (this PR). What do you think?

One concern would be backward compatibility, if those changes aren't compatible with minitest 5 then we should do a major gem version release.

[rmm5t]

@thibaudgg With #165 merged and a planned 2.x release of guard-minitest ahead of merging this PR, I think this PR is now lined up well to prepare for a later 3.x release. That way, we maintain backwards compatibility in 2.x while being able to look forward with 3.x releases.

/cc @rymai