CI: Upgrade to FreeBSD 14.3

FreeBSD 14.3 was released on June 10, 2025:

https://www.freebsd.org/releases/14.3R/announce/

(backport <rust-lang#4642>)
(cherry picked from commit d54af17)

Author: neuschaefer

.cirrus.yml

@@ -18,7 +18,7 @@ task:
         image_family: freebsd-13-4
     - name: nightly freebsd-14 x86_64
       freebsd_instance:
-        image: freebsd-14-2-release-amd64-ufs
+        image: freebsd-14-3-release-amd64-ufs
     - name: nightly freebsd-15 x86_64
       freebsd_instance:
        image_family: freebsd-15-0-snap