testdriver-vendor.js is currently not effectively using async/await, and it also seems to have a few buggy promise resolutions.
<rdar://problem/102613798>
Pull request: https://github.com/WebKit/WebKit/pull/6746
Committed 257030@main (5f95c4f4489d): <https://commits.webkit.org/257030@main> Reviewed commits have been landed. Closing PR #6746 and removing active labels.