[Perl/perl5] 1557e6: 19207: Document ellipsis statement error

[Joe McMahon via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: 1557e6c32831defe4b25a924a88baf5f5e7bcbdd
      
https://github.com/Perl/perl5/commit/1557e6c32831defe4b25a924a88baf5f5e7bcbdd
  Author: Joe McMahon <joe.mcma...@gmail.com>
  Date:   2022-10-24 (Mon, 24 Oct 2022)

  Changed paths:
    M .mailmap
    M pod/perldiag.pod

  Log Message:
  -----------
  19207: Document ellipsis statement error

Adds a section to `perldiag` that details what the `Unimplemented` error
is, caused by executing an ellipsis ("...;") statement.