Retag v6.9.0

Created by: robertd

Can you guys re-tag v6.9.0 since without this commit new users will be confused on how to upgrade.

Also I would suggest adding bundle exec rake gitlab:satellites:create RAILS_ENV=production to the upgrade guide. In my case I actually had to use it like 3 upgrades in a row. I'll whip up a PR later on.

Thanks