reprotest: pipes module will be removed in Python 3.13

pipes.quote() was already deprecated in Python 2.7 but silently got
aliased to `shlex.quote()`. Python 3.13 removes the `pipes` module and
thus the alias.

Signed-off-by: Jelle van der Waa <jelle@archlinux.org>
Signed-off-by: Holger Levsen <holger@layer-acht.org>