Change forum link from private to public

The handbook has a link for the private announcements forum in the following places:

• https://handbook.opencraft.com/en/latest/roles/list/#communication
• https://handbook.opencraft.com/en/latest/open_first/#thats-a-lot-to-follow

The first time I was on the onboarding course, looking at the handbook, I did not have my forum account yet. As an anonymous user, the page looks like this:

I suggest that we use the public announcements forum for these two links. Not sure if the context of the page relates exclusively to the private announcements forums.