ci: fix check for Ubuntu 20.04
In
5ca0c455f1 (ci: fix Python dependency on Ubuntu 24.04, 2024-05-06),
we made the use of Python 2 conditional on whether or not the CI job
runs Ubuntu 20.04. There was a brown-paper-bag-style bug though, where
the condition forgot to invoke the `test` builtin. The result of it is
that the check always fails, and thus all of our jobs run with Python 3
by accident.
Fix this.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>