[Perl/perl5] 113cef: threads.xs: Set non thread context in ithread_set()

[Karl Williamson via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: 113cefaa4a736b299757774019cd1ee97b7e2db9
      
https://github.com/Perl/perl5/commit/113cefaa4a736b299757774019cd1ee97b7e2db9
  Author: Karl Williamson <k...@cpan.org>
  Date:   2023-04-04 (Tue, 04 Apr 2023)

  Changed paths:
    M dist/threads/threads.xs

  Log Message:
  -----------
  threads.xs: Set non thread context in ithread_set()

This generally was getting set anyway, but a test yet to be committed
found a case where it wasn't.