Docs: Add a @staticvar entry for $first_dropdown in WP_Widget_Categories::widget().

Props ajayghaghretiya1.
Fixes #41473.

git-svn-id: https://develop.svn.wordpress.org/trunk@41181 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/widgets/class-wp-widget-categories.php

@@ -35,6 +35,8 @@ class WP_Widget_Categories extends WP_Widget {
 	 *
 	 * @since 2.8.0
 	 *
+	 * @staticvar bool $first_dropdown
+	 *
 	 * @param array $args     Display arguments including 'before_title', 'after_title',
 	 *                        'before_widget', and 'after_widget'.
 	 * @param array $instance Settings for the current Categories widget instance.