add mono

Author: kevinjqliu

dev/tasks/python-wheels/github.osx.yml

@@ -51,7 +51,7 @@ jobs:
 
       - name: Install System Dependencies
         run: |
-          brew install bash bison coreutils ninja
+          brew install bash bison coreutils ninja mono
           echo "$(brew --prefix bison)/bin" >> $GITHUB_PATH
 
       - name: Homebrew packages