Bump the edition since why not

Signed-off-by: Alex Saveau <saveau.alexandre@gmail.com>

Author: SUPERCILEX

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name        = "nix"
 description = "Rust friendly bindings to *nix APIs"
-edition     = "2018"
+edition     = "2021"
 version     = "0.26.1"
 rust-version = "1.63"
 authors     = ["The nix-rust Project Developers"]