I don't think we need to provide a way to silence it.  Consider that we've never before supported not having the file type inferrence.  There are no 2.x suites that depend on the the file type not being inferred.  If they want to tag their specs explicitly instead of relying on this, they can set it temporarily while going through the upgrade process, and then remove the config setting and switch to explicit tagging after they are on 3.0.  In fact, I think it would be a bad idea to do the 2.x => 3.0 upgrade and the change to tagging at the same time: it introduces 2 massive changes at once, and when something goes wrong it'll be unclear what it was that caused the problem.  Much better to do them one at a time.

We can also word the deprecation message so that we tell users they can freely ignore the deprecation warning if they do not want the file type inferrence behavior.  We've done it before:

https://github.com/rspec/rspec-core/blob/b20d96189c770b5f83f16d03c9c6dceab080be31/lib/rspec/core/example_group.rb#L85-L88