Reduce severity of auth provider warning

Summary:
Ref T7208. Now that we have approvals (new installs are safe by default), take those into account when generating this warning.

Try to soften the warning to cover the case discussed in T7208, hopefully without requiring additional measures.

Test Plan:

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T7208

Differential Revision: https://secure.phabricator.com/D11708