tests/helper-runtests.sh

remotefilelog: actually fix (and test this time) a bytes vs str issue

I attempted this in 94670e124d29 but we didn't actually have any tests for this
function it seems, and I mistook "it works now" for it being fixed (when what
had actually happened was that my cache had populated enough that I didn't
trigger the minimum threshold on my reattempts).

Differential Revision: https://phab.mercurial-scm.org/D7785

#
# Avoid interference from actual test env:

unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL