Document how to make public GitHub API requests without rate limits for self-hosted Enterprise runners

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Feature description

I am running Dependabot with a self-hosted runner on a GitHub Enterprise server, and during the action run I see a number of mentions of API requests being rate limited to public github.com when it reaches out for things such as patch notes etc:

`API rate limit exceeded for X (But here's the good news: Authenticated requests get a higher rate limit. Check out the documentation for more details.) // See: https://docs.github.com/rest/overview/resources-in-the-rest-api#rate-limiting`

What is not clear to me is _how_ I provide the Dependabot runner with credentials to public GitHub. Do I need to provide a personal access token within a specifically named environment variable on the machine where the runner is setup, or do I need to provide it with some additional credentials elsewhere such as in the actions secret menu? The docs the warning links to does not provide any instructions for this, nor the actual Dependabot docs themselves.

I found this [issue which seems related](https://github.com/dependabot/dependabot-core/issues/3024), but adding a environment variable called `GITHUB_ACCESS_TOKEN` or `LOCAL_GITHUB_ACCESS_TOKEN` with a fine-grained PAT from my github.com service account to the machine's .env file where my action runner is configured still results in the rate limiting warning.

Depending on the size of the project these rate limits cause Dependabot to take quite some time to complete as it results in the job getting held up. Would it be possible to document this (if not done already) if there is a known way around? All I can find are a number of issues with solutions that don't seem to work.

Start with the Dependabot documentation and the linked issue #3024, then verify how public github.com API credentials are configured for self-hosted Enterprise runners. Document the supported credential location and variable name, including whether a PAT or actions secret is required, and confirm the setup prevents the reported rate-limit warning.

Written by the indexing model from the issue text.