ci: update FreeBSD cirrus job

ci: update FreeBSD cirrus job

FreeBSD 12 is EOL and no longer available, causing errors in this job.

Upgrade to 13.2, which is the next oldest release with support and that
should keep it for at least another 4 months.

This will be upgraded again once 13.3 is released to avoid further
surprises.

The original report [*] of this problem mentions an error message
"Not enough compute credits to prioritize tasks!".  It seems to be
just a reminder that the credit allocate for the Free Tier by Cirrus
is all used up and which might result in additional delays getting a
result.

[*] https://lore.kernel.org/git/d2d7da84-e2a3-a7b2-3f95-c8d53ad4dd5f@gmx.de/

Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>