Turns out that the root cause is that automake no longer depends on autopoint, and adding it as an explicit dependency fixed it.
MR pending approval at https://salsa.debian.org/debian/xz-utils/-/merge_requests/10
- Bug#1150841: xz-utils: autopkgtest needs update... Paul Gevers
- Processed: xz-utils: autopkgtest needs upd... Debian Bug Tracking System
- Bug#1150841: xz-utils: autopkgtest needs u... Otto Kekäläinen
- Bug#1150841: xz-utils: autopkgtest nee... Otto Kekäläinen
