[PubSub] subscription.on_error is called indefinitely without backoff

#### Environment details

- OS: linux
- Ruby version: 3.2.2
- Gem name and version: google-cloud-pubsub

#### Steps to reproduce

1. create a project, topic, and subscription
2. start a subscriber
3. delete the project

#### Code example

```
subscription.listen { ... }
subscription.on_error { |e| p err }
```

When the subscription is not found, `on_error` is called without backoff (almost every ms). It might be a good idea to add not found error to this clause.

https://github.com/googleapis/google-cloud-ruby/blob/24cf55114d6e727d2ca0afe93513a98841f704ee/google-cloud-pubsub/lib/google/cloud/pubsub/subscriber/stream.rb#L287-L289

#### Full backtrace

> 5:Requested project not found or user does not have access to it (project=project-id-here). Make sure to specify the unique project identifier and not the Google Cloud Console display name.. debug_error_string:{UNKNOWN:Error received from peer ipv4:173.194.192.95:443 {created_time:"2023-05-02T07:10:56.589985506+00:00", grpc_status:5, grpc_message:"Requested project not found or user does not have access to it (project=project-id-here). Make sure to specify the unique project identifier and not the Google Cloud Console display name."}}

```
/usr/local/bundle/gems/grpc-1.53.0-x86_64-linux/src/ruby/lib/grpc/generic/active_call.rb:29:in `check_status'
/usr/local/bundle/gems/grpc-1.53.0-x86_64-linux/src/ruby/lib/grpc/generic/bidi_call.rb:211:in `block in read_loop'
/usr/local/bundle/gems/grpc-1.53.0-x86_64-linux/src/ruby/lib/grpc/generic/bidi_call.rb:197:in `loop'
/usr/local/bundle/gems/grpc-1.53.0-x86_64-linux/src/ruby/lib/grpc/generic/bidi_call.rb:197:in `read_loop'
/usr/local/bundle/bin/whatever:in `each'
```