Fix PHPStan missingType.generics for Prophecy not specifying its type

Problem/Motivation

Fix

ignoreErrors[] = [
	'message' => '#^Method Drupal\\\\Tests\\\\jsonapi\\\\Kernel\\\\Normalizer\\\\JsonApiTopLevelResourceNormalizerTest\\:\\:doProphesize\\(\\) return type with generic class Prophecy\\\\Prophecy\\\\ObjectProphecy does not specify its types\\: T$#',
	'identifier' => 'missingType.generics',
	'count' => 1,
	'path' => __DIR__ . '/modules/jsonapi/tests/src/Kernel/Normalizer/JsonApiTopLevelResourceNormalizerTest.php',
];

and similar.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet