Do not run merge queue tests on tier 2 x86_64-apple-darwin

x86_64-apple-darwin has been demoted to tier 2 since Rust 1.90.
Moreover, Github runners for macOS 14 on x86_64 are much slower than the
others.

Author: samueltardieu

.github/workflows/clippy_mq.yml

@@ -25,8 +25,6 @@ jobs:
           host: i686-unknown-linux-gnu
         - os: windows-latest
           host: x86_64-pc-windows-msvc
-        - os: macos-14
-          host: x86_64-apple-darwin
         - os: macos-latest
           host: aarch64-apple-darwin