Bump MSRV to 1.76

```
error: package `toml_writer v1.0.6+spec-1.1.0` cannot be built because it requires rustc 1.76 or newer, while the currently active rustc version is 1.75.0
```

Author: taiki-e

Cargo.toml

@@ -3,7 +3,8 @@ name = "macrotest"
 version = "1.2.0"
 authors = ["eupn <eupn@protonmail.com>"]
 edition = "2021"
-rust-version = "1.66"
+# NB: Sync with README.md and src/lib.rs.
+rust-version = "1.76"
 license = "MIT OR Apache-2.0"
 readme = "README.md"
 repository = "https://github.com/eupn/macrotest"

README.md

@@ -9,7 +9,7 @@
 
 Similar to [trybuild], but allows you to test how declarative or procedural macros are expanded.
 
-*Minimal Supported Rust Version: 1.66*
+*Minimal Supported Rust Version: 1.76*
 
 ----
 

src/lib.rs

@@ -4,7 +4,7 @@
 //!
 //! Similar to [trybuild], but allows you to write tests on how macros are expanded.
 //!
-//! *Minimal Supported Rust Version: 1.66*
+//! *Minimal Supported Rust Version: 1.76*
 //!
 //! <br>
 //!