CirrusCI recently introduced [1] new feature to use image families
instead of bare image names for gCloud based instances.
This allows us to use most recent stable builds. All the stable builds
are in the same image family in gCloud and it will run instances using
the most recent one.
This also allows us to simply use 11.3 image instead of 11.2. There
was no such ability previously, because base freebsd-11-3-release-amd64
image has issues[2] that doesn't allow CirrusCI to use it. However,
later stable 11.3 images from freebsd-11-3-snap family works fine.