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

Branch
------
REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/bfc1bd4a0f732b8c31be11f03ff0f86ee87ee118

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