Update Rust version to 1.71 in Cargo.toml

Author: taiki-e

Cargo.toml

@@ -3,7 +3,7 @@ name = "async-signal"
 version = "0.2.12"
 edition = "2021"
 authors = ["John Nunley <[email protected]>"]
-rust-version = "1.63"
+rust-version = "1.71"
 description = "Async signal handling"
 license = "Apache-2.0 OR MIT"
 repository = "https://github.com/smol-rs/async-signal"