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@gmail.com>
Discussion: https://postgr.es/m/CAN55FZ3_P4JJ6tWZafjf-_XbHgG6DQGXhH-y6Yp78_bwBJjcww@mail.gmail.com

Branch
------
REL_16_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/49389240bb5e8a3f18a72a41323c0d4c64add38b

Modified Files
--------------
.cirrus.tasks.yml | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)