t0021: test filter metadata for additional cases

t0021: test filter metadata for additional cases

Check that we get the expected data when performing a merges or
generating archives.  Note that we don't expect a ref for merges,
because we won't be checking out any particular ref, but instead a tree
of the merged data.  For archives, however, we expect a ref as normal if
we have one.

Signed-off-by: brian m. carlson <redacted>
Signed-off-by: Junio C Hamano <redacted>