Add back 429 to list of retryable requests (#1599)

* add back 429 to list of retryable requests

* fix lint error

src/internal/shared/artifact-twirp-client.ts

@@ -132,7 +132,8 @@ class ArtifactHttpClient implements Rpc {
       HttpCodes.BadGateway,
       HttpCodes.GatewayTimeout,
       HttpCodes.InternalServerError,
-      HttpCodes.ServiceUnavailable
+      HttpCodes.ServiceUnavailable,
+      HttpCodes.TooManyRequests
     ]
 
     return retryableStatusCodes.includes(statusCode)