On ESR[60] stub installer isn't designed to work, and we expect most users of esr will have no use for a stub installer. However this poses some problems where the taskgraph assumes that any Nightly generates a stub installer and thus it should be available along the way.
The patch hardcodes the list of branches that do not need a stub installer, though we'll want to clean up this specification in some way, as Thunderbird will likely need it to be cleaner and we may want on-change builds to use this logic (e.g. for on-change l10n).
Differential Revision: https://phabricator.services.mozilla.com/D1082
