Update FreeBSD 13 CI image

FreeBSD 13.2 will be EoL in about a month.

Author: asomers

.cirrus.yml

@@ -1,7 +1,7 @@
 task:
   name: nightly x86_64-unknown-freebsd-13
   freebsd_instance:
-    image_family: freebsd-13-2
+    image_family: freebsd-13-3
   setup_script:
     - pkg install -y libnghttp2 curl
     - curl https://sh.rustup.rs -sSf --output rustup.sh