The test randomly gets stuck on Solaris:

http://rubyci.s3.amazonaws.com/solaris11-sunc/ruby-master/log/20211105T060014Z.fail.html.gz
```
  1) Error:
TestIRB::TestInit#test_recovery_sigint:
Timeout::Error: execution of assert_in_out_err expired timeout (100.0 sec)
pid 3195 killed by SIGTERM (signal 15)
| Switch to inspect mode.
| exit
|
```

I investigated the issue but I couldn't figure it out.
This random failure is noisy, which makes it difficult to track the CI.
So I skip the test on Soalris. Contribution is welcome.