Upgrade dev dependencies: credo, ex_doc, dialyxir

[JuneKelly]

Upgrade:

• credo 1.7
• ex_doc 0.30
• dialyxir 1.3

This will close some of those pesky dependabot issues.

[JuneKelly]

Incidentally, I think we have some (caching?) issues in CI:

This kind of failure was fixed in #60, and the tests all pass locally. I'll look into this.

EDIT: I now wonder if the tests still fail sporadically in one of the environments in the test matrix, which I just now realised exists.

[epinault]

Hm.. strange . 22.04 and latest elixir seems strange to fail

[epinault]

maybe we just punt on 22.? because seems to be that 23 and 24 have been there long enough at this point

[JuneKelly]

Sorry it's taken a while to get back to this, I've been busy 😅

Sure, I agree, let's just test on 23 and 24, if we can't figure this out easily.