Tests: Add missing @covers tag for a wp_update_comment() test.

Follow-up to [37609], [53863].

See #56793.

git-svn-id: https://develop.svn.wordpress.org/trunk@55320 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/comment.php

@@ -1142,6 +1142,9 @@ class Tests_Comment extends WP_UnitTestCase {
 		}
 	}
 
+	/**
+	 * @covers ::wp_update_comment
+	 */
 	public function test_update_should_invalidate_comment_cache() {
 		global $wpdb;