Auto merge of #3028 - asomers:fbsd12.4, r=JohnTitor

Update FreeBSD 12 CI environment to 12.4

12.3 will soon be EoL.

Author: bors

.cirrus.yml

@@ -1,7 +1,7 @@
 task:
   name: nightly x86_64-unknown-freebsd-12
   freebsd_instance:
-    image: freebsd-12-3-release-amd64
+    image: freebsd-12-4-release-amd64
   setup_script:
     - pkg install -y curl
     - curl https://sh.rustup.rs -sSf --output rustup.sh