autopkgtest-build-qemu uses vmdb2 >= 0.22 to build at least qemu-system images. This means at least bullseye, since older debian had older vmdb2. And in bullseye and up, qemu-debootstrap is just a trivial wrapper for debootstrap command, the only extra action it does is to print a deprecation warning, that's all.
Here, debootstrap (and qemu-debootstrap) are used on the "build" system, not on the target system where the actual autopkgtests will be run. So it's fine to assume the image-build-tools are to be from more recent distributions than the test-target images are. It is perfectly okay to drop usage of qemu-debootstrap now and run debootstrap directly. But this is not only in autopkgtest but in vmdb2 too (filing a bug against it now). Meanwhile, I re-introduced qemu-debootstrap wrapper in 8.1.0+ds-5 qemu, to unbreak at least some things. Thanks, /mjt
