Fix build installation on mac to make platform-specific wheel rather than universal one

Author: jobovy

.github/workflows/build.yml

@@ -283,7 +283,8 @@ jobs:
     - name: Install package
       if: matrix.os == 'macos-latest'
       run: |
-        python -m pip install -v .
+        # Everything --platform etc. necessary to make sure to make a non-universal wheel (universal binary wheel doesn't work, because the GSL isn't universal)
+        python -m pip install -v . --platform=`uname -m` --no-deps --target=`python -m site --user-site`
     - name: Special config
       env:
           TEST_FILES: ${{ matrix.TEST_FILES }}