Tests: Use more specific assertions in image saving tests.

When passed a `WP_Image_Editor` instance as the `$image` parameter, `wp_save_image_file()` returns an array on success, so we can specifically check for an array instead of any non-empty result.

Likewise, in PDF tests, when creating an attachment is expected to return an integer ID and not a `WP_Error` object, we can specifically check for that.

Follow-up to [1061/tests], [38949], [39617], [42792], [53529], [53530], [53531], [55019], [55066].

See #56793.
Built from https://develop.svn.wordpress.org/trunk@55070


git-svn-id: http://core.svn.wordpress.org/trunk@54603 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.2-alpha-55069';
+$wp_version = '6.2-alpha-55070';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.