Track fixing version for otrs2 via buster

Note the upload cannot be done via unstable as the new upstream version
did contain many changes which would be not be possible at this point of
the release to gate via unstable to testing.

Maintainer filled an unblock request as per [1], which was acked by the
release team already.

Assuming maintainer will perform now the upload an remove the moreinfo
tag, and the version will land in buster, already start tracking the
version.

 [1] https://bugs.debian.org/928223