Dependabot v2 bundler: private registries url option structure

I’m confused by the url structure for private registries in Dependabot v2. For example with rubygems-server:

    type: rubygems-server
    token: ${{secrets.MY_GITHUB_PERSONAL_TOKEN}}

If I understand correctly, octocat in that example is the GitHub user/org, but then what role does github_api serve in that example? Is that a private repository? Is it a directory like you would specify under updates elsewhere? It’s not clear from the example what URL paths are supported or expected for the url option.