tests/helper-runtests.sh

py3: use '%d' for integers rather than '%s'

obsolete._readmarkers() returns an integer version number.

Differential Revision: https://phab.mercurial-scm.org/D1537

#
# Avoid interference from actual test env:

unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL