CI: use macOS 14 instead of GitHub-deprecated macOS 13 in merge queue checks (#16032)

The "macos 13" runners are being phased out
(actions/runner-images#13046).

Some jobs have started to fail in the CI while attempting a merge
because of the brownout period.

changelog: none

r? flip1995

Author: flip1995

.github/workflows/clippy_mq.yml

@@ -25,7 +25,7 @@ jobs:
           host: i686-unknown-linux-gnu
         - os: windows-latest
           host: x86_64-pc-windows-msvc
-        - os: macos-13
+        - os: macos-14
           host: x86_64-apple-darwin
         - os: macos-latest
           host: aarch64-apple-darwin