CI: Downgrade to FreeBSD 13.3

A bugreport seems to indicate that segfaults in rustc are less likely on
FreeBSD 13.3.

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=285873

Author: neuschaefer

.cirrus.yml

@@ -12,10 +12,10 @@ task:
       env:
         TARGET: i686-unknown-freebsd
       freebsd_instance:
-        image_family: freebsd-13-4
+        image_family: freebsd-13-3
     - name: nightly freebsd-13 x86_64
       freebsd_instance:
-        image_family: freebsd-13-4
+        image_family: freebsd-13-3
     - name: nightly freebsd-14 x86_64
       freebsd_instance:
         image: freebsd-14-3-release-amd64-ufs