web-platform-tests/wpt merge_pr_47417

on GitHub

part2 : always return a promise.

According to [1], the requestConstructors should always return a
promise.

[1] https://searchfox.org/mozilla-central/rev/dd421ae14997e3bebb9c08634633a4a3e3edeffc/testing/web-platform/tests/encrypted-media/util/drm-messagehandler.js#190-205

Differential Revision: https://phabricator.services.mozilla.com/D217846

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1909952
gecko-commit: 96d5ea6637134156a4a740eb6874d834c6b064c3
gecko-reviewers: media-playback-reviewers, padenot