ci: fix persistent macOS clang_rt.osx linker failure (stale target cache)

The real cause was not a flaky runner image: the macOS Test job restored a
cached `target/` built against a previous runner Xcode, and that stale build
dir carried a clang compiler-rt search path (.../clang/<N>/lib/darwin) that no
longer exists on the current image, so the linker failed with
'ld: library clang_rt.osx not found' on every commit.

Fix: stop caching `target/` on the test job (cache only the download-heavy
registry/git dirs) and bump the cache key to v2 to discard the poisoned
caches. Also deleted the existing poisoned macOS caches. Reverted the macos-14
pin (it didn't help and that image is deprecating) back to macos-latest, which
is fine now that target/ is always built clean.

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-14
+            os: macos-latest
             archive: tar.gz
             cargo_flags: "--no-default-features --features ort-dynamic,vector-search"
           - target: aarch64-apple-darwin
-            os: macos-14
+            os: macos-latest
             archive: tar.gz
             cargo_flags: ""