feat: raise embedded-io-async's MSRV to 1.81

This is the same MSRV as embedded-io, which embedded-io-async depends on.

Author: mkroening

embedded-io-async/Cargo.toml

@@ -2,7 +2,7 @@
 name = "embedded-io-async"
 version = "0.6.1"
 edition = "2021"
-rust-version = "1.75"
+rust-version = "1.81"
 description = "Async embedded IO traits"
 repository = "https://github.com/rust-embedded/embedded-hal"
 readme = "README.md"