REST: Avoid making 'wpaccuracy' required in API requests
Some configs can have this particular argument absent in the request.
For example defining different accuracy levels:
$wgFlaggedRevsTags = [
'accuracy' => [ 'levels' => 1, 'quality' => 20, 'pristine' => 21 ],
In such a case, requiring this as a boolean fails hence it should not be
hard required. It's in this case optional.