ci: Bump FreeBSD to 15.0.

Author: fraggerfox

.github/workflows/ci.yml

@@ -270,7 +270,7 @@ jobs:
         - name: Compile
           uses: vmactions/freebsd-vm@v1
           with:
-            release: '14.3'
+            release: '15.0'
             usesh: true
             prepare: |
               pkg install -y gmake autoconf automake pkgconf git