Add minimal version 1.67.0 of rustc to the package.

This is due to the usage of usize::ilog10()[1] in description::Description.

[1] https://doc.rust-lang.org/std/primitive.usize.html#method.ilog10

PiperOrigin-RevId: 515614142

Author: bjacotg

README.md

@@ -25,8 +25,7 @@ This library brings the rich assertion types of Google's C++ testing library
  * A new set of assertion macros offering similar functionality to those of
    [GoogleTest](https://google.github.io/googletest/primer.html#assertions).
 
-**We recommend using Rust 1.66 or later with this library.** It does not work
-smoothly with prior versions.
+**The minimum supported Rust version is 1.67**
 
 > :warning: The API is not fully stable and may still be changed until we
 > publish version 1.0.

googletest/Cargo.toml

@@ -22,6 +22,7 @@ repository = "https://github.com/google/googletest-rust"
 readme = "../README.md"
 license = "Apache-2.0"
 edition = "2021"
+rust-version = "1.67.0"
 authors = [
   "Bradford Hovinen <hovinen@google.com>",
   "Bastien Jacot-Guillarmod <bjacotg@google.com>",