Fix lint: add copyright header

Author: nicojs

packages/jest-core/src/runCore.ts

@@ -1,3 +1,10 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
 import exit = require('exit');
 import {CustomConsole} from '@jest/console';
 import type {AggregatedResult, TestContext} from '@jest/test-result';