This PR fixes a regression where goals that don't exist were being
displayed. The regression was triggered by #5835 and originally caused
by #4926.
Bug originally reported at
https://leanprover.zulipchat.com/#narrow/channel/270676-lean4/topic/tactic.20doesn't.20change.20primary.20goal.20state/near/488957772.
The cause of this issue was that #5835 made certain `SourceInfo`s
canonical, which was directly transferred to several `TacticInfo`s by
#4926. The goal state selection mechanism would then pick up these extra
`TacticInfo`s.
The approach taken by this PR is to ensure that the `SourceInfo` that is
being transferred by #4926 is noncanonical.
