Switch to xhyve for the FreeBSD VM

For reasons unknown, the VM fails to start up when using qemu, even
though it worked fine before. Per
cross-platform-actions/action#80, it seems
this may also affect other users.

.github/workflows/freebsd.yml

@@ -28,6 +28,6 @@ jobs:
           version: '14.0'
           memory: 8G
           environment_variables: 'CARGO_HOME LIBRARY_PATH CARGO_REGISTRIES_CRATES_IO_PROTOCOL'
-          hypervisor: qemu
+          hypervisor: xhyve
           image_url: 'https://github.com/inko-lang/freebsd-builder/releases/download/v0.7.0/freebsd-14.0-x86-64.qcow2'
           run: ./ci/freebsd.sh