Remove irb from test dependeicy and from test matrix

[tompng]

Reline's test no longer depends on irb.

CI was failing in ruby 2.6 because github:ruby/irb requires ruby >= 2.7

Could not find compatible versions

Because every version of irb depends on Ruby >= 2.7
  and Gemfile depends on irb >= 0,
  Ruby >= 2.7 is required.
So, because current Ruby version is = 2.6.10,
  version solving has failed.

https://github.com/ruby/reline/actions/runs/4678386950/jobs/8287063665?pr=532

[ima1zumi]

Oh, are you removing IRB tests?
I think we aren't running it due to dependencies. I think we aimed to ensure IRB isn't broken by Reline changes, as it's the main user.

[ima1zumi]

There was a PR that started to run IRB tests on CI.
#53

At that time, they were running IRB tests because it was difficult to test terminal emulators.
I think we could remove IRB tests now that we have yamatanooroti.

[tompng]

Reline is already not using irb in tests and the test matrix using irb had no effect. Test depending on irb was removed in #502

Before that, reline was requiring irb only to use RubyLex for calculating number of autoindent and code termination. I think it was not testing/ensuring integrity of irb and reline.

[st0012]

Although it's not the intention, I feel it could still help capturing compatibility issues with IRB? Like if there's a PR that'd break IRB, it's probably already merged when we detect it on the IRB side, which means we'll need additional work to revert/patch the change.

I understand that ideally we should decouple reline's tests from IRB, but the reality is that IRB still is the biggest reline user, which provides the coverage we can use. Although debug also uses reline, it disable reline in tests.

How about we put this test in its own workflow and give it its own Ruby matrix that matches IRB's requirement?

[tompng]

I see and I agree. I will revert the workflow. 🙇