Raise required compiler to 1.81

Required by `home` since 0.5.11.

    error: package `home v0.5.11` cannot be built because it requires rustc 1.81 or newer, while the currently active rustc version is 1.74.1
    Either upgrade to rustc 1.81 or newer, or use
    cargo update home@0.5.11 --precise ver
    where `ver` is the latest version of `home` supporting rustc 1.74.1

Author: dtolnay

.github/workflows/ci.yml

@@ -24,7 +24,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [nightly, beta, stable, 1.74.0]
+        rust: [nightly, beta, stable, 1.81.0]
         os: [ubuntu]
         include:
           - name: macOS

Cargo.toml

@@ -10,7 +10,7 @@ edition = "2021"
 keywords = ["cargo", "subcommand", "macros"]
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/dtolnay/cargo-expand"
-rust-version = "1.70"
+rust-version = "1.81"
 
 [features]
 default = ["prettyplease"]