composefs: Bump composefs max version to 1

composefs: Bump composefs max version to 1

This generates the new format for whiteout markers which was added in
6.8 (and which will be backported to 6.7). Without this whiteouts
will not work anymore.

This is a slight format change, but will only affect ostree commits
that already were broken (i.e that had whiteouts), and since the
composefs code is still marked experimental I think it is fine to
do this without introducing another format version on the ostree
side.

Signed-off-by: Alexander Larsson <alexl@redhat.com>