tests: adapt now that Mercurial clears the merge state for empty wdir `hg evolve` forgot to clear the merge state when its attempt to commit resulted in no commit because the working copy had no changes. That resulted in test-evolve-issue5967.t showing a conflict state that shouldn't be there. The responsibility for clearing the merge state was moved into Mercurial in Mercurial in 6a34e438461b (commit: clear resolved mergestate even if working copy is clean, 2020-02-28), so the bug is now fixed in `hg evolve`, which impacts that test case. CORE-TEST-OUTPUT-UPDATE: 6a34e438461b