The anaconda upload token is a secret on github (nudles).
If the secret is not available, no uploading.
Note: github ci cannot access the secret directly within the `if` check;
you have to assign it to a env var first and then do if check;
better do the upload on push (not on pull request).

Add the CI to run on MacOS, including building, testing pysinga and
uploading the package to anaconda if the token is available.

Fix the permission issue conda/conda#7267
and the sdk issue.
The sdk is fixed to the latest version (in conda_build_config.yaml).
The python is fixed to 3.6 to be compatible with colab.