CI: update target FreeBSD version to 14.3 (#2271)

FreeBSD VM setup is unhappy unless we
target the latest minor version.

Author: kinkie

.github/workflows/slow.yaml

@@ -144,7 +144,7 @@ jobs:
     strategy:
       matrix:
         osversion:
-          - 14.2
+          - 14.3
 
     runs-on: ubuntu-24.04
     name: freebsd(${{ matrix.osversion }})