quinn: hide implicit feature for optional smol dependency

Author: djc

quinn/Cargo.toml

@@ -36,7 +36,7 @@ rustls-ring = ["dep:rustls", "ring", "proto/rustls-ring", "proto/ring"]
 # Outside wasm*-unknown-unknown targets, this enables `Endpoint::client` and `Endpoint::server` conveniences.
 ring = ["proto/ring"]
 runtime-tokio = ["tokio/time", "tokio/rt", "tokio/net"]
-runtime-smol = ["dep:async-io", "smol"]
+runtime-smol = ["dep:async-io", "dep:smol"]
 
 # Configure `tracing` to log events via `log` if no `tracing` subscriber exists.
 tracing-log = ["tracing/log", "proto/tracing-log", "udp/tracing-log"]