So as highlighted by
https://github.com/hyperium/tonic/issues/730#issuecomment-895635088 it
turns out the new `Interceptor` trait required changes to tonic-build as
well, which I forgot to publish yesterday. Didn't see it because it wasn't
clear from the commit message.

So this bumps tonic _and_ tonic-build to 0.5.2 so we can release both.
There are no code changes.