runtests: use deterministic sort for TESTINFO lines

Sort TESTINFO lines by description within the number of skipped test.
It makes the list of skipped test groups easier to diff/compare between
jobs and runs.

Closes #15374

tests/runtests.pl

@@ -3147,7 +3147,7 @@ if(%skipped && !$short) {
         $log_line .= ")\n";
         $restraints{$log_line} = $skip_count;
     }
-    foreach my $log_line (sort {$restraints{$b} <=> $restraints{$a}} keys %restraints) {
+    foreach my $log_line (sort {$restraints{$b} <=> $restraints{$a} || uc($a) cmp uc($b)} keys %restraints) {
         logmsg $log_line;
     }
 }