[util-chroot] use C.UTF-8 by default
- systemd >= 251 is forcing nspawns to use LANG=C.UTF-8: https://github.com/systemd/systemd/commit/b626f6959bcee11d966f96bd29a00502f4aa2ce4
- It makes sense to generate the C.UTF-8 locate here when using it as the default LANG value.
- based on: https://gitlab.manjaro.org/yochananmarqos1/manjaro-chrootbuild/-/commit/30067144dbcb7dc4bda145923be88e0432c3d608