[Perl/perl5] a93c91: MB_CUR_MAX is C89, change comment accordingly

[Karl Williamson via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: a93c9128eb1306fc15c7b25040919300ce889d03
      
https://github.com/Perl/perl5/commit/a93c9128eb1306fc15c7b25040919300ce889d03
  Author: Karl Williamson <k...@cpan.org>
  Date:   2023-12-22 (Fri, 22 Dec 2023)

  Changed paths:
    M locale.c

  Log Message:
  -----------
  MB_CUR_MAX is C89, change comment accordingly

Spotted by Tony Cook.