Make sure we have (array) on the return of the filter.

Co-authored-by: Evan Herman <[email protected]>

checks/readme.php

@@ -91,7 +91,7 @@ function check_for_warnings() {
 		 * @param array  $ignored_warnings Array of ignored warning keys.
 		 * @param Parser $readme The readme object.
 		 */
-		$ignored_warnings = apply_filters( 'plugin_check_readme_warnings_ignored', $ignored_warnings, $this->readme );
+		$ignored_warnings = (array) apply_filters( 'plugin_check_readme_warnings_ignored', $ignored_warnings, $this->readme );
 
 		$warning_keys = array_diff( $warning_keys, $ignored_warnings );