Recap: git's new check in "git hash-object" breaks some tests in src:dgit, which deliberately create broken objects eg to detect a regression like #849041. Updating the tests looks nontrivial.
git 1.2.40-1 doesn't seem like it's going to migrate anyway, given that it's a key package which was uploaded during the freeze, and the git maintainer hasn't filed an unblock. My previous message didn't receive any response and we're well into the hard freeze. I therefore don't have any plans to update dgit's test suite for bookworm. I have taken this work item off my personal todo lists and tracking machinery, including suppressing the nag emails that I usually get when my autopkgtests are blocking some other package. After the bookworm release, the severity of this bug should probably be raised. That will put this issue back on my radar. Thanks, Ian.