Fix failing test.

[reitermarkus]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

---

CI is broken because example.com doesn't return an Accept-Ranges header anymore. We shouldn't actually curl it anyways in tests.

[carlocab]

Suggested change

	supports_partial = headers&.key?("accept-ranges") && headers["accept-ranges"] != "none"
	supports_partial = headers.fetch("accept-ranges", "none") != "none"

But you'll need to return {} after ErrorDuringExecution above.