conform/conformtest.pl: Escape literal braces in regular expressions

This suppresses Perl warnings like these:

Unescaped left brace in regex is deprecated here (and will be fatal in
Perl 5.32), passed through in regex; marked by <-- HERE in m/^element
*({ <-- HERE ([^}]*)}|([^{ ]*)) *({([^}]*)}|([^{ ]*)) *([A-Za-z0-9_]*)
*(.*)/ at conformtest.pl line 370.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
(cherry picked from commit ddb3c626)