bundlerepo: use suffix variable
It looks like the refactor in 702a26fec3e2 attempted to establish
this method argument but failed to use it. My editor caught it.
Differential Revision: https://phab.mercurial-scm.org/D1373
#
# Avoid interference from actual test env:
unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL