Fixes the following error caught by the Node.js CI:

../deps/v8/src/api.cc:8943:10:
  error: no viable conversion from returned value of type
  'unique_ptr<v8::internal::MicrotaskQueue, default_delete<v8::internal::MicrotaskQueue>>'
  to function return type
  'unique_ptr<v8::MicrotaskQueue, default_delete<v8::MicrotaskQueue>>'

  return microtask_queue;
         ^~~~~~~~~~~~~~~

Change-Id: Ic09dab46bb8f87a2b3b59f5836e0883bfe0e9681
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1627533
Commit-Queue: Michaël Zasso <mic.besace@gmail.com>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61789}