Fix MacOS wheel builds.

Homebrew was recently updated
(actions/runner-images#2415),
introducing a bug related to 2to3:
actions/runner-images#2428. I applid
the workaround recommended in the issue.

build_scripts/wheels/macos.sh

@@ -6,6 +6,8 @@ brew update
 python -V
 brew install -v bison || brew upgrade bison
 brew install -v cmake || brew upgrade cmake
+# temporary workaround for https://github.com/actions/virtual-environments/issues/2428
+rm -rf /usr/local/bin/2to3
 brew install -v ninja || brew upgrade ninja
 python -m pip install -U pip setuptools wheel
 CMAKE_PREFIX_PATH="$(brew --prefix bison)"