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
syntax: re
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^html/
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~$
\.swp$
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^tests/.*\.err$
^tests/easy_run.sh$
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tests/\.testtimes
^docs/training/graphs/
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^docs/training/index.html
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^docs/training/img/
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