Fixeszsh-users/zsh-syntax-highlighting#262.
Currently, 'make quiet-test' uses Perl. However, since it is considered a development
tool rather than a user-facing tool, users and downstream packages needn't install Perl.
Furthermore, even this dev-only dependency may be dropped in the future.
The only difference between tests/tap-filter here and the one in the issue is using
a `cat` subshell v. using 'undef $/; <STDIN>'.