(maint) Bump version to 6.9.0-SNAPSHOT
(maint) Bump version to 6.9.0-SNAPSHOT

Since we accidentally didn't ship the new JRuby pool in 6.8.0, the next release
will also need to be a feature (Y) release.

puppetlabs/puppet-server,puppetlabs/puppetserver,puppetlabs/puppet-server,puppetlabs/puppetserver,puppetlabs/puppetserver,puppetlabs/puppetserver,puppetlabs/puppet-server