GitHub v1 detector: ignore matches in `avatars.githubusercontent.com` URLs

[rgmz]

The GitHub v1 detector matches results from the avatars.githubusercontent.com domain, resulting in a large amount of false positives.

Example

      {
        github: "zpinto",
        name: "Zachary Pinto",
        shortname: "Zach",
        university: "University of California, Irvine",
        city: "Irvine",
        avatar: "https://avatars3.githubusercontent.com/u/20071182?s=460&u=df311dec2adab597c9b1727638a5385eac7ceadb&v=4",
        url: "/preview-template/campus-experts/campus-experts.github.io/pr/3628zpinto"
      },
      {
        github: "ionicc",
        name: "Sagar Vakkala",
        shortname: "Sagar",
        university: "SRM Institute of Science and Technology",
        city: "Chennai",
        avatar: "https://avatars2.githubusercontent.com/u/19570480?s=400&u=390ab557b5dbe9add852b0a4cb807a1b1d5717a0&v=4",
        url: "/preview-template/campus-experts/campus-experts.github.io/pr/3628ionicc"
      },

or
https://github.com/linkedin/li-langchain/blob/5395c254d584103123a140eaa91b1fa49ddadd78/docs/data/people.yml#L2258