Otherwise we reset DNS configuration to empty after failing to collect
base OS configuration from dns.noopManager, e.g.
```
2025/05/08 05:48:08 wgengine: Reconfig: configuring DNS
2025/05/08 05:48:08 dns: Set: {DefaultResolvers:[] Routes:{cat-ray.ts.net.:[] ts.net.:[199.247.155.53 2620:111:8007::53]}+65arpa SearchDomains:[cat-ray.ts.net.] Hosts:50}
2025/05/08 05:48:08 health(warnable=dns-read-os-config-failed): error: Tailscale failed to fetch the DNS configuration of your device: getting OS base config is not supported
2025/05/08 05:48:08 health(warnable=dns): error: getting OS base config is not supported
2025/05/08 05:48:08 [v1] authReconfig: ra=false dns=true 0x00: getting OS base config is not supported
2025/05/08 05:48:08 [v1] authReconfig: ra=false dns=true 0x00: <nil>
```
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