Deal with a whole lot of PHPStan suppressed key casting errors

closes #6534

tests/phpunit/utils/TestCloningRegistry.php

@@ -37,9 +37,13 @@ final class TestCloningRegistry{
 
 	/**
 	 * @return \stdClass[]
+	 * @phpstan-return array<string, \stdClass>
 	 */
 	public static function getAll() : array{
-		/** @var \stdClass[] $result */
+		/**
+		 * @var \stdClass[] $result
+		 * @phpstan-var array<string, \stdClass> $result
+		 */
 		$result = self::_registryGetAll();
 		return $result;
 	}