Auto merge of #2759 - asomers:fbsd12.3, r=Amanieu

Update FreeBSD 12 CI image to 12.3.  12.2 is EoL.

11.4 is also EoL, but we need to keep testing on FreeBSD 11 since we
expose a FreeBSD 11 ABI.

.cirrus.yml

@@ -16,7 +16,7 @@ task:
 task:
  name: nightly x86_64-unknown-freebsd-12
  freebsd_instance:
- image: freebsd-12-2-release-amd64
+ image: freebsd-12-3-release-amd64
  setup_script:
  - pkg install -y curl
  - curl https://sh.rustup.rs -sSf --output rustup.sh