tests: fix style issue of importing order in test-lock.py
test-lock.py is excluded in test-check-module-imports.t, because
import-checker.py reports that some stdlibs are imported after local
silenttestrunner module.
I can not found out any reason why tests/silenttestrunner.py should be
imported before some stdlibs from the point of functionality view.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}