mkosi: update debian commit reference

mkosi: update debian commit reference

* aa17b7ddf9 Fix stage1 build
* 2c13391e33 Update changelog for 256.5-1 release
* 7d13196926 autopkgtest: skip TEST-64-UDEV-STORAGE due to qemu crash
* 47769e8d7c Drop patch merged upstream
*   4e8e9315b5 Update upstream source from tag 'upstream/256.5'
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| * 71b885347d New upstream version 256.5
* 89a33e5408 d/e/checkout-upstream: undo quilt patches before switching debian branch
* 3c942ecb0d d/e/checkout-upstream: do not rebase on main when building stable branches