[Perl/perl5] f72873: gh18842: fix a pair of sprintf format warnings

[Hugo van der Sanden via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: f72873660d1db9867dbdc98bbfc9e52b63387937
      
https://github.com/Perl/perl5/commit/f72873660d1db9867dbdc98bbfc9e52b63387937
  Author: Hugo van der Sanden <h...@crypt.org>
  Date:   2021-05-31 (Mon, 31 May 2021)

  Changed paths:
    M perl.c

  Log Message:
  -----------
  gh18842: fix a pair of sprintf format warnings

The format is '%s', so it is not appropriate to wrap the char * arguments
in SVfARG().