As noted in #140, we're getting renovate MRs asking to upgrade to Django
6.0 which is a non-LTS release. We have an `allowOnlyLTSDjango` preset
available intended for use in these cases. Make use of it both in the
generated template (to avoid downstream MR creation) and in this project
(to avoid bumping the version in new templates).

Closes #148

feat: prevent upgrades to non-LTS Django releases

Closes #148

See merge request !161