.arcconfig

tests: show invalid copies when turning off copies-in-changeset

If you turn on copies in changesets and write a commit with a copy,
then turn it off and amend the commit while undoing the copy, the
invalid copy information will remain. The read path doesn't crash in
invalid copy data, but it seems better to not produce the invalid
data.

Differential Revision: https://phab.mercurial-scm.org/D6751

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