Replace "can support 2xx HTTP status (other than 200)" test

The test `can support 2xx HTTP status (other than 200)` occasionally fails because it's relying on an external server that seems to have spotty availability. This causes CI to someone fail for no good reason. We should update this test to spy/mock the XHR request so that it doesn't need to access the network at all.

Locate the test named `can support 2xx HTTP status (other than 200)` and inspect how its XHR request reaches the external server. Replace the network dependency with an XHR spy or mock, then run the relevant test to confirm it passes without network access and still checks the 2xx response behavior.

Written by the indexing model from the issue text.