pgsql: ci: Upgrade FreeBSD image

ci: Upgrade FreeBSD image

Upgrade to the current stable version. To avoid needing commits like this in
the future, the CI image name now doesn't contain the OS version number
anymore.

Backpatch to all versions with CI support, we don't want to generate CI images
for multiple FreeBSD versions.

Author: Nazir Bilal Yavuz <byavuz81(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAN55FZ3_P4JJ6tWZafjf-_XbHgG6DQGXhH-y6Yp78_bwBJjcww@mail.gmail.com
Backpatch-through: 15

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/ad40644eb8582fc1f537330b76ae7893cacf7b21

Modified Files
--------------
.cirrus.tasks.yml | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)