push: use "repo['.']" instead of old form "repo['']"
Note that this does not conflict with the commit message of my
previous patch: I found this after writing the previous patch
(besides, I very easily forget things).
Differential Revision: https://phab.mercurial-scm.org/D2965
#
# Avoid interference from actual test env:
unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL