Tests: Use correct post_author value in WP_Test_REST_Attachments_Controller.

The `$editor_id` property is declared as static, so can only be approached as static, even when used within the same class in which the property is declared.

Using non-static access will result in `null`. See: https://3v4l.org/93HQL

This PHP notice was hidden so far, due to the existence of magic methods in the `WP_UnitTestCase_Base` class.

All the same, the magic methods as they were, would also return `null` for this property. All in all, the attachment being created for this test would never get the correct `post_author`.

Fixed by using static access to approach the static property.

This bug was discovered while fixing (removing) the magic methods in the `WP_UnitTestCase_Base` class in an effort to improve compatibility with PHP 8.2.

Follow-up to [38832].

Props jrf, costdev, johnbillion.
See #55652.

git-svn-id: https://develop.svn.wordpress.org/trunk@54041 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/rest-api/rest-attachments-controller.php

@@ -1079,7 +1079,7 @@ class WP_Test_REST_Attachments_Controller extends WP_Test_REST_Post_Type_Control
 			array(
 				'post_mime_type' => 'image/jpeg',
 				'post_excerpt'   => 'A sample caption',
-				'post_author'    => $this->editor_id,
+				'post_author'    => self::$editor_id,
 			)
 		);