With this in place, all `-j`obs will not run by default on try. This will omit
such jobs in most try pushes even if files-changed matches. This is
unfortunate, but better than running them unconditionally. Fuzzy selections,
and later `just try it` pushes, are the ultimate solution here.
With this change, a push with no try syntax or try_task_config.json will schedule
no tasks at all.
MozReview-Commit-ID: FGjqlDW1FT6