fix test failure with git version 2.34.0

fix test failure with git version 2.34.0

The new "ort" resolver uses different filenames than what the test suite
accepted when resolving a conflict between a directory an an annexed
file. Make the test looser in what it accepts, so it will work with old
and new git.

Other tests still look for "conflictor.variant" as a prefix,
because when eg resolving a conflicted merge of 2 annexed files,
the filename is not changed by the ort resolver, and I didn't want to
unncessarily loosen the test.

Also I'm not entirely happy with the filenames used by the ort resolver,
see comment.

There's still another test failure caused by that resolver that is not
fixed yet.