Agent fails to reconnect with 401 Invalid access token after being offline for long periods of time

One of my Buildkite agents spends a lot of time asleep. Often when I wake it after several days of sleeping, the agent process fails to reconnect and the log fills up with entries like this:

```
...
2020-07-14 21:53:04 WARN Desktop PC Failed to ping: GET https://agent.buildkite.com/v3/ping: 401 Invalid access token (Last successful was 116h25m52.6913959s ago)
2020-07-14 21:53:05 WARN Desktop PC POST https://agent.buildkite.com/v3/heartbeat: 401 Invalid access token (Attempt 2/5 Retrying in 5s)
...
```

Restarting the agent process fixes the issue, but I think the agent should be able to recover from this condition instead of simply retrying the invalid access token indefinitely.

Buildkite agent v3.22.1, Windows 10 build 19041.329