Microtasks policy should not be updated for the renderer because
`NodeBindings::CreateEnvironment` might be entered with or without
`UvRunOnce()` on stack. One of the examples of such calls is
`window.open()` which is possible to invoke while `uv_run()` is still
running (e.g. with `setImmediate()`).

All in all, it doesn't matter that much which policy we use since
`v8::MicrotasksScope` has a check for the policy in its destructor and
no commits will be made if the policy is `kExplicit`. It is important,
however, to not change the policy in the middle of `UvRunOnce()` so we
should respect whatever we currently have and move on.

Fix: #29463