fix async stacktraces getting clobbered

Author: connor4312

src/vs/workbench/api/test/common/extensionHostMain.test.ts

@@ -63,6 +63,7 @@ suite('ExtensionHostMain#ErrorHandler - Wrapping prepareStackTrace can cause slo
 		}]
 	);
 
+	const originalPrepareStackTrace = Error.prepareStackTrace;
 	const insta = new InstantiationService(collection, false);
 
 	let existingErrorHandler: (e: any) => void;
@@ -81,6 +82,10 @@ suite('ExtensionHostMain#ErrorHandler - Wrapping prepareStackTrace can cause slo
 		findSubstrCount = 0;
 	});
 
+	teardown(() => {
+		Error.prepareStackTrace = originalPrepareStackTrace;
+	});
+
 	test('basics', function () {
 
 		const err = new Error('test1');