Skip io/wait tests for methods deleted in Ruby 4

[XrXr]

See: ruby/io-wait#49

---

Note that you probably want to also make changes to https://github.com/ruby/rbs/blob/master/core/io/wait.rbs to remove ready? and nread. I'm not sure the best way to go about it would be, though.

[ksss]

@XrXr
The next version of RBS v4 is planned to be released after Ruby v4.

The target version for RBS signatures follows the latest Ruby as follows:
https://github.com/ruby/rbs?tab=readme-ov-file#the-target-version

If methods does not exist at Ruby v4, please remove the signature and testing.

[ksss]

@XrXr I have taken the liberty of removing the type definition on my end.
#2710

[XrXr]

Thanks!

[nobu]

The next version of RBS v4 is planned to be released after Ruby v4.

Then Ruby 4.0.0 will bundle RBS 3.9.5?

[ksss]

@nobu We're planning to bundle RBS v3.10 with Ruby v4.

[nobu]

@ksss Thank you