mkosi: update arch commit reference

mkosi: update arch commit reference

* 8160e63e52 Limit logic required for building locally
* 3a62443e41 OBS build: add support for xz and zst compression formats
* 9667464ad7 Get rid of _tag variable
* 73dc492b5e upgpkg: 257.2-2: rebuild with changes for service restart
* 6b7355b5bb do not restart any templated units
* 332718f955 exclude vmspawn units from restart as well
* 5a749a6716 exclude systemd-nspawn@* services from restart
* 8a10796f8b upgpkg: 257.2-1: new upstream release
* 16294a0b44 Add support for building from git in OBS
* 38b664eed4 upgpkg: 257.1-1: new upstream release
* e26158dda9 upgpkg: 257-1: new upstream release
* c984b75c3f restart services after upgrade...
* 27fae2c192 upgpkg: 256.9-1: new upstream release
* 1afdd08a60 upgpkg: 256.8-2: apply: shutdown: close DM block device before issuing DM_DEV_REMOVE ioctl