From VonC's answer to the same question asked on SuperUser:
Both in their announcement and in the help section, this (tag) doesn't seem to be available (at the time of the writing of this answer).
That means GitHub for Mac doesn't manage yet the tags namespace (refs/tags), and that you need to tag manually, and then git push --tags
to GitHub also manually.
Though that was a year ago, there's still nothing to indicate that tags are supported. There's still no mention in the help section, subsequent blog posts about it don't mention tags, nor do the release notes (though they only cover relatively recent versions).