Attempt to workaround worker thread termination crash

See discussion in nodejs/node#38418

lib/fork.js

@@ -3,6 +3,7 @@ import {fileURLToPath} from 'url';
 import {Worker} from 'worker_threads';
 
 import Emittery from 'emittery';
+import pEvent from 'p-event';
 
 import {controlFlow} from './ipc-flow-control.cjs';
 
@@ -31,8 +32,14 @@ const createWorker = (options, execArgv) => {
 			stderr: true
 		});
 		postMessage = worker.postMessage.bind(worker);
+
+		// Ensure we've seen this event before we terminate the worker thread, as a
+		// workaround for https://github.com/nodejs/node/issues/38418.
+		const starting = pEvent(worker, 'message', ({ava}) => ava && ava.type === 'starting');
+
 		close = async () => {
 			try {
+				await starting;
 				await worker.terminate();
 			} finally {
 				// No-op

lib/worker/base.js

@@ -222,6 +222,7 @@ const onError = error => {
 };
 
 if (isRunningInThread) {
+	channel.send({type: 'starting'}); // AVA won't terminate the worker thread until it's seen this message.
 	const {options} = workerData;
 	delete workerData.options; // Don't allow user code access.
 	run(options).catch(onError); // eslint-disable-line promise/prefer-await-to-then