Add missing async-io feature in gix-packetline-blocking

Otherwise there would be many unexpected_cfgs warnings for async-io
coming from the gix-packetline sources.

Author: Urgau

gix-packetline-blocking/Cargo.toml

@@ -19,6 +19,9 @@ default = ["blocking-io"]
 ## If set, all IO will become blocking. The same types will be used preventing side-by-side usage of blocking and non-blocking IO.
 blocking-io = []
 
+## DO NOT USE, use instead directly gix-packetline
+async-io = []
+
 #! ### Other
 ## Data structures implement `serde::Serialize` and `serde::Deserialize`.
 serde = ["dep:serde", "bstr/serde"]