Only run clang-format in ubuntu

Author: cacharle

.github/workflows/ci.yml

@@ -133,6 +133,7 @@ jobs:
         echo "LIBZMQ=${PWD}/libzmq-build" >> ${GITHUB_ENV}
 
     - name: format
+      if: ${{ startsWith(matrix.os, 'ubuntu') }}
       run: |
         clang-format --version
         git ls-files | grep -E '\.(cpp|hpp)' | xargs clang-format --dry-run --Werror