When reviewing https://phabricator.services.mozilla.com/D288166 I noticed the order between `await waitForSetOverride;` and `await writeTextContentToPath(OVERRIDDEN_SCRIPT, path);` was the opposite of our other helper, but I didn't think this could matter. It's actually critical to wait until `waitForSetOverride` is complete, because this action will attempt to write the file once, with the initial content from the response. Differential Revision: https://phabricator.services.mozilla.com/D295404