configure: fix rust meson configuration

It was incorrectly set on the [host_machine] and caused error:
File "/tmp/qemu-test/build/pyvenv/lib/python3.11/site-packages/mesonbuild/envconfig.py", line 281, in from_literal
    assert all(isinstance(v, str) for v in raw.values()), 'for mypy'
AssertionError: for mypy

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20250924120426.2158655-7-marcandre.lureau@redhat.com>
1 file changed