ci: pin macOS runners to macos-14 (fix flaky clang_rt.osx linker failure)

The rolling macos-latest image intermittently ships a broken compiler-rt
path, causing 'ld: library clang_rt.osx not found' on the Rust link step of
an otherwise-green commit (a README-only change failed CI this way). Pinning
all five macOS jobs (CI test + CI release-build + Release) to macos-14 gives a
stable Xcode/clang toolchain so the linker step is deterministic.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/release.yml

@@ -39,11 +39,11 @@ jobs:
           # consumers must `brew install onnxruntime` before running — see
           # INSTALL-INTEL-MAC.md bundled in the tarball.
           - target: x86_64-apple-darwin
-            os: macos-latest
+            os: macos-14
             archive: tar.gz
             cargo_flags: "--no-default-features --features ort-dynamic,vector-search"
           - target: aarch64-apple-darwin
-            os: macos-latest
+            os: macos-14
             archive: tar.gz
             cargo_flags: ""