[Perl/perl5] 0b8457: Add a regex test for changes in 1d8aafa

[E. Choroba]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: 0b8457c08dcbd23afba5c33a382bbc4e4c04d8cd
      
https://github.com/Perl/perl5/commit/0b8457c08dcbd23afba5c33a382bbc4e4c04d8cd
  Author: E. Choroba <chor...@matfyz.cz>
  Date:   2021-05-20 (Thu, 20 May 2021)

  Changed paths:
    M t/re/re_tests

  Log Message:
  -----------
  Add a regex test for changes in 1d8aafa

In https://groups.google.com/u/1/g/google-code/c/bn4X3d-89to, Neil
Agarwal wrote:

---

Could someone please explain to me the output of the following Perl
code in Code Jam's test run mode? The system gives "BCD" instead of
"ABCD", and I have not been able to reproduce this behavior anywhere
else.

$S1 = "1((((((7(9))))))";
$S2 = "1((((((7(9)))))";

print "A" if $S1 =~ /[89]+/;
print "B" if $S1 =~ /[9]+/;
print "C" if $S2 =~ /[89]+/;
print "D" if $S2 =~ /[9]+/;

---

I tried to bisect the problem and discovered the wrong behaviour was
introduced in 2813d4adc971fbaa124b5322d4bccaa73e9df8e2 and fixed in
1d8aafa0548097ffe407cad078f79b4d56fd7dca, which means all 5.28.* had
this problem. Google Code Jam used 5.28.1 in the 2021 contest.

This commit adds the original test case to prevent further
regressions.