Disable cross-clang32 build

Likely forever (with MSYS2 toolchain); perhaps we will get some other alternatives in the future.

(cherry picked from commit fb6b2f9)

.github/workflows/build_test.yml

@@ -292,7 +292,11 @@ jobs:
            disable_tests:
              - ButteraugliTest.Lossless
              - ButteraugliTest.Distmap
-         - msystem: clang32
+         # "Legacy" toolchains are being "phased-out":
+         # https://www.msys2.org/news/#2023-12-13-starting-to-drop-some-32-bit-packages
+         # clang32 is already missing required "gtest" and "libavif"
+         # - msystem: clang32
+         #   disable_benchmark: true
 
     defaults:
       run: