ci/freebsd: bump freebsd version to 15.1

Author: llyyr

.github/workflows/build.yml

@@ -538,7 +538,7 @@ jobs:
       uses: cross-platform-actions/action@v1.3.0
       with:
         operating_system: freebsd
-        version: '15.0'
+        version: '15.1'
         run: |
             sudo pkg update
             sudo pkg install -y \