Repro of inability to call GitHub from Cloudflare Workers. Solution: This can be solved by adding the "User-Agent" header to calls.

index.ts

/**
 * @description This is the entry point for the Cloudflare Worker.
 * Call it with `http://0.0.0.0:8787?endpoint=gh` or `http://0.0.0.0:8787?endpoint=swapi`
 */
export default {
  async fetch(request: Request): Promise<Response> {
    const { searchParams } = new URL(request.url);
    let endpoint = searchParams.get("endpoint");

    const result = await (async () => {
      if (endpoint === "gh") return await callGitHub();
      if (endpoint === "swapi") return await callSwapi();
      return "Add an endpoint in the form of either '?endpoint=gh' or '?endpoint=swapi'!";
    })();

    return end(result);
  },
};

/**
 * @description Convenience wrapper for fetching data from GitHub.
 */
async function callGitHub() {
  return await fetchData(
    "https://api.github.com/repos/facebook/react/stats/participation",
    {
      headers: {
        Accept: "application/vnd.github.v3+json",
        "User-Agent": "GitHub API Client for Cloudflare Workers"
      },
    }
  );
}

/**
 * @description Convenience wrapper for fetching data from SW API.
 */
async function callSwapi() {
  return await fetchData("https://swapi.dev/api/people/1");
}

/**
 * @description Handle fetching data.
 */
async function fetchData(url: string, options?: Record<string, any>) {
  return fetch(url, {
    method: "GET",
    ...(options || {}),
  })
    .then((res: any) => {
      console.log("Status:", res.status);
      console.log("Headers:", JSON.stringify(Object.fromEntries(res.headers)));
      if (res.status === 200) return res.json();
      return "";
    })
    .catch((error: any) => {
      console.error(error);
      return error?.message || "Unknown error";
    });
}

/**
 * @description Send back JSON response.
 */
function end(result: string | Record<string, any>) {
  const json = JSON.stringify(
    {
      result,
    },
    null,
    2
  );

  return new Response(json, {
    headers: {
      "Content-Type": "application/json",
    },
  });
}