bolt currently FTBFS during dh_auto_test and also fails its autopktest. This is due to a change in systemd v251. See https://github.com/systemd/systemd/issues/23499 where this is being discussed.
I've created a MR. See https://salsa.debian.org/freedesktop-team/bolt/-/merge_requests/5
This is no longer and issue with umockdev 0.17.3 See https://github.com/martinpitt/umockdev/commit/ed55f28285bf12a90068a4def6ae13270dfe4df3 Thus closing the bug report