rustls-ffi version doesn't match what curl itself says it uses

https://github.com/curl/curl/blob/curl-8_0_1/docs/RUSTLS.md says:

> This version of curl depends on version v0.9.2 of rustls-ffi.

But curl-sys depends on 0.8.

That being said, I'm seeing problems with both 0.8 and 0.9 (both using rustls 0.20) that seem to be fixed in 0.10 (rustls 0.21).