tests: demonstrate obsmarker creation after discarding conflicting changes
Continued evolve creates an incorrect obsmarker that says 2 is a successor of
1. It's incorrect because 1 was dropped as it created no changes to commit
(after conflict resolution that discarded its changes).
If evolve does the same thing in one go (e.g. just by using --tool :local and
without subsequent need to continue) the obsmarker is correct.