mkosi: update debian commit reference to a8ad8e30e70c0b82ecb8fe016f2dde3a084236f0

mkosi: update debian commit reference to a8ad8e30e70c0b82ecb8fe016f2dde3a084236f0

* a8ad8e30e7 Stop installing legacy sysv tools/units for upstream builds
* 9856b1b1bd Install new files for upstream build
* b68bfb52d4 Update changelog for 257.7-2 release
* 3bd5f6d2e0 systemd-boot-tools: change architecture to linux-any
* 057ce29542 Move bootctl zsh completion file too to new package
* b47be01659 Revert "Revert installing systemd-networkd-varlink.socket"
* 71a425dd3b ukify: recommend sbsigntool | pesign for signing
* 54f67475ee Revert installing systemd-networkd-varlink.socket