[Perl/perl5] 6eba35: Document warning on previous declaration of 'field...

[James E Keenan via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: 6eba35fced89a113ca937adab5c9ef60ca6862c1
      
https://github.com/Perl/perl5/commit/6eba35fced89a113ca937adab5c9ef60ca6862c1
  Author: James E Keenan <jkee...@cpan.org>
  Date:   2023-12-31 (Sun, 31 Dec 2023)

  Changed paths:
    M pod/perldiag.pod

  Log Message:
  -----------
  Document warning on previous declaration of 'field' variable

Fixes GH #21783.