ci: Bump FreeBSD VM to 15.1

The FreeBSD:15 package repo now ships rust built against 15.1's libc,
so cargo fails to start on 15.0:

  /lib/libc.so.7: version FBSD_1.9 required by /usr/local/bin/cargo not found

Signed-off-by: Daniel Schaefer <dhs@frame.work>

Author: JohnAZoidberg

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
       id: test
       uses: vmactions/freebsd-vm@v1
       with:
-        release: "15.0"
+        release: "15.1"
         arch: x86_64
         usesh: true
         mem: 8192