phases: make `allphases` a list on py3 also
Pytype complained that `range` doesn't support slicing, so make this a list like
it was on py2.
Differential Revision: https://phab.mercurial-scm.org/D7468
#
# Avoid interference from actual test env:
unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL