install openMP on macos

.github/workflows/python-package.yml

@@ -40,6 +40,11 @@ jobs:
           echo "CC=gcc-10" >> $GITHUB_ENV
           echo "CXX=g++-10" >> $GITHUB_ENV
 
+      - name: Set up macOS environment
+        if: runner.os == 'macOS'
+        # openMP isnt part of core apple clang for some reason?
+        run: brew install openmp
+
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip