TAP tests for psql \g piped into program

Hi,

This is a follow-up to commit d2a44904 from the 2022-11 CF [1]
The TAP tests were left out with the suggestion to use Perl instead of
cat (Unix) / findstr (Windows) as the program to pipe into.

PFA a patch implementing that suggestion.


[1] https://commitfest.postgresql.org/40/4000/

Best regards,
--
Daniel Vérité
https://postgresql.verite.pro/
Twitter: @DanielVerite