* actions: don't recommend users allow-list our hosted runners
There are too many IP addresses for our hosted runners for users to use
them as an allow-list. In fact, we have a note where we _don't_
recommend that they use this. Remove a contradictory sentence below.
* ip addresses: clarify what these ip addresses are
* self-hosted: clarify inbound/outbound requirements
* Update content/actions/hosting-your-own-runners/about-self-hosted-runners.md
* Update content/authentication/keeping-your-account-and-data-secure/about-githubs-ip-addresses.md
Co-authored-by: hubwriter <hubwriter@github.com>