Split brain: Always push the maintainer view tag

Our algorithm for calculating whether to do a pseudomerge to make the
dgit view fast forward from the archive contents depends on the
maintainer view tag (effectively, it uses it to go back from the
archive contents dgit view back to the corresponding maintainer view).

So we need to push it too.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>