🧪 Testing: Fill in unit tests!

[JoshuaKGoldberg]

Bug Report Checklist

• I have tried restarting my IDE and the issue persists.
• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

The initial commit for this repo has approximately zero unit test coverage 😄:

describe("githubSponsorsToMarkdown", () => {
	it("exists", () => {
		expect(githubSponsorsToMarkdown).toBeDefined();
	});
});

Let's add tests!

Additional Info

I'm pretty flexible here: as long as the test runs githubSponsorsToMarkdown and asserts the results look reasonable, I'm generally happy. The one trick is that the unit tests should not make network calls. They'll need to mock out the network call done by await graphqlWithAuth in some way, such as with a vitest module mock.