tests: accept new bzr message about switching branches
The new version apparently prints "Switched to branch at " instead of
"Switched to branch: ".
Differential Revision: https://phab.mercurial-scm.org/D8106
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}