FormUrlencodedValidator incorrectly expects object for the schema

[mpviau]

Using oneOf on a schema for a form-url-encoded body does not work.

It throws this exception:

vendor/league/openapi-psr7-validator/src/PSR7/Validators/BodyValidator/FormUrlencodedValidator.php(54): League\OpenAPIValidation\Schema\Exception\TypeMismatch::becauseTypeDoesNotMatch(Array, NULL)

It look like the check has been copy/pasted from the multi part body validator, which I am not using.