Streaming pull subscriber does not notify of loss of network

- OS: Ubuntu 22.04
- Node.js version: 18.16.0
- npm version: 9.5.1
- `@google-cloud/pubsub` version: 3.7.1

#### Steps to reproduce

1. Call PubSub.subscription(), and then setup on() handlers for 'message', 'debug', 'error', and 'close'
2. After initiating the initial subscription and receiving some streaming pull messages, disconnect the network on the machine
3. Notice that there are no error or debug events of any kind after several minutes. In other words, there is no notice of the fact that the network is gone and the subscription pull is therefore no longer operating. If the network is disconnected before the streaming pull begins, then there are debug messages and eventually there is an error after the default 5 minute timeout where the subscription is closed. But none of this happens if the network disconnects after the stream has been established.