ci: update Perforce version to r23.2

ci: update Perforce version to r23.2

Update our Perforce version from r21.2 to r23.2. Note that the updated
version is not the newest version. Instead, it is the last version where
the way that Perforce is being distributed remains the same as in r21.2.
Newer releases stopped distributing p4 and p4d executables as well as
the macOS archives directly and would thus require more work.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>