Disable macos on GitHub Actions
Disable macos on GitHub Actions

PyCall requires that Python is build with `--enable-shared` option.
GitHub Action's macOS image has Python but it isn't build with
`--enable-shared`, so PyCall cannot be tested on that environment.

mrkn/pycall,mrkn/pycall.rb,mrkn/pycall,mrkn/pycall.rb,mrkn/pycall.rb,mrkn/pycall.rb,mrkn/pycall,mrkn/pycall