https://phab.mercurial-scm.org/D7252 (5d40317d42b7083b49467502549e25f144888cb3)
introduced a regression in Rust tests.

This is a temporary fix that replicates the behavior of the C and Python impl,
pending the resolution of the discussion (in the phabricator link) about how
we actually want to solve this problem.

Differential Revision: https://phab.mercurial-scm.org/D7503