CI: Build macOS FIPS202 sanitizer tests with clang 22

The macos-latest label has migrated to the macOS 26 (Tahoe) arm64 image,
whose default-toolchain ASan runtime (nixpkgs clang 21.x) deadlocks at
process startup: compiler-rt's shadow-memory init re-enters the
uninitialized allocator. This made the AArch64 FIPS202 backend_tests job
hang until the 6h job timeout, intermittently, depending on which image a
matrix leg landed on. Same symptom as python/cpython#145199.

The fix landed upstream in LLVM >= 22 (llvm/llvm-project#191039, backported
as #192082). Point the macOS sanitizer job at the existing 'clang22' dev
shell so it builds with clang 22 and can run on macos-latest again.

Signed-off-by: Hanno Becker <beckphan@amazon.co.uk>

Author: hanno-becker

.github/workflows/ci.yml

@@ -157,7 +157,12 @@ jobs:
       - name: build + test
         uses: ./.github/actions/multi-functest
         with:
-          nix-shell: 'ci'
+          # clang 22 shell: the default `ci` shell's clang 21 ASan runtime
+          # deadlocks at process startup on the macos-latest / macOS 26 (Tahoe)
+          # image (compiler-rt shadow-memory init; same symptom as
+          # python/cpython#145199), fixed in LLVM >= 22 by
+          # llvm/llvm-project#191039 (backport #192082).
+          nix-shell: 'clang22'
           nix-cache: 'false'
           gh_token: ${{ secrets.GITHUB_TOKEN }}
           compile_mode: 'native'