fix: ready and error events are allowed wihtin sub workers

Author: simllll

src/index.ts

@@ -56,7 +56,7 @@ export class Agenda extends EventEmitter {
 	on(event: 'ready', listener: () => void): this;
 	on(event: 'error', listener: (error: Error) => void): this;
 	on(event: string, listener: (...args) => void): this {
-		if (this.forkedWorker && event !== 'ready') {
+		if (this.forkedWorker && event !== 'ready' && event !== 'error') {
 			const warning = new Error(`calling on(${event}) during a forkedWorker has no effect!`);
 			console.warn(warning.message, warning.stack);
 			return this;