close 959631 thanks i was not able to reproduce this via git-pbuilder. also, as of today, the ci-builds [1] pass nicely (they failed for two weeks between 2020-05-01 and 2020-05-10 (incl.) which is when this bug was reported).
since this doesn't seem to be an issue any longer, i'm closing this. [1] https://ci.debian.net/packages/h/hy/
