install ninja from pip instead of brew

Author: karosc

.github/workflows/build_wheel.yml

@@ -106,8 +106,6 @@ jobs:
         with:
           package-dir: ./swmm-toolkit
         env:
-          # mac needs ninja to build
-          CIBW_BEFORE_BUILD_MACOS: brew install ninja
           # configure cibuildwheel to build native archs ('auto'), and some emulated ones      
           CIBW_ARCHS_LINUX: aarch64
           CIBW_ARCHS_MACOS: arm64