Docs: Add missing variable reference for `wp_edit_form_attachment_display`.

This adds the missing `$post` reference in the inline docblock for
the `wp_edit_form_attachment_display` hook after [37879].

Props DrewAPicture.
See 36052.

git-svn-id: https://develop.svn.wordpress.org/trunk@37880 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/media.php

@@ -2773,7 +2773,7 @@ function edit_form_image_editor( $post ) {
 		 *
 		 * @since 4.6.0
 		 *
-		 * @param WP_Post A post object.
+		 * @param WP_Post $post A post object.
 		 */
 		do_action( 'wp_edit_form_attachment_display', $post );