mkosi: update debian commit reference to 6f15bdaae7014c233b662ac4a33d464893b81b36

mkosi: update debian commit reference to 6f15bdaae7014c233b662ac4a33d464893b81b36

* 6f15bdaae7 Update architecture match for 50-pid-max.conf (v3)
* 333cc1fcc5 Downgrade depends to recommends for IPC endpoint of respective libnss modules
* ab99a1b51a Revert "Update architecture match for 50-pid-max.conf"
* b93d7f855a Update changelog for 259~rc3-1 release
* 95c7f8a3d6 Install new udev rule
* 89509d9692 d/t/tests-in-lxd: re-construct --pin-packages arguments for autopkgtest
* 6b77249c71 d/extra/dbus-1: rename systemd-localed-read-only.conf
* 819831c19a Update architecture match for 50-pid-max.conf
* 0ddff89e9d Mirror dmi_arches from meson.build into debian/udev.install
* 398e8791db d/t/control: pull in optional libs for boot-and-services too
* c727922ad5 Update changelog for 259~rc2-1 release
* 8faf105531 Install new varlinkctl bash completion script
* f4b4cea2be d/t/control: ensure unit-tests autopkgtest pulls in dlopened libraries for test
* 7e8aba9883 Update changelog for 259~rc1-1 release
* 5953c42402 Update symbols file for v259~rc1
* 353125ccfa Install new files for v259~rc1
* ca22d1ca4f Drop patches, all merged upstream
* 32c75efca2 d/t/unit-config: fix python decorator copypasta
* e32179d633 d/rules: disable sysv compat in upstream builds
* cf77bd44be Install new files for upstream build
* aa564e5d3b kernel-install: skip 55-initrd.install when an initrd is already staged