t6423: expect improved conflict markers labels in the ort backend

t6423: expect improved conflict markers labels in the ort backend

Conflict markers carry an extra annotation of the form
   REF-OR-COMMIT:FILENAME
to help distinguish where the content is coming from, with the :FILENAME
piece being left off if it is the same for both sides of history (thus
only renames with content conflicts carry that part of the annotation).
However, there were cases where the :FILENAME annotation was
accidentally left off, due to merge-recursive's
every-codepath-needs-a-copy-of-all-special-case-code format.

Update a few tests to have the correct :FILENAME extension on relevant
paths with the ort backend, while leaving the expectation for
merge-recursive the same to avoid destabilizing it.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>