`cmd/getroughtime -config ecosystem.json` failing to get responses from cloudflare

version: 460d2331427e85ce88a03d2c8c7d734f62d483cd

Observe that only time.txryan.com succeeds, and Cloudflare-Roughtime-2 is failing.

```
$ go run cmd/getroughtime/main.go -config ecosystem.json
skipped Cloudflare-Roughtime-2: protocol: response is missing NONC tag
skipped int08h-Roughtime: no reply
skipped roughtime.se: no reply
time.txryan.com: 2026-04-24 00:38:36 +0000 UTC ±3s (in 263ms)
Delta: -901ms
```

I expected at least cloudflare-roughtime-2 would have a successful result.

I looked a bit more into this. I see `roughtime.cloudflare.com:2003` does return a good result if the ping-version is `Google-Roughtime`:

```
$ go run cmd/getroughtime/main.go -ping roughtime.cloudflare.com:2003 -pubkey 0GD7c3yP8xEc4Zl2zeuN2SlLvDVVocjsPSL8/Rl/7zg= -ping-version Google-Roughtime
Ping response: 2026-04-24 00:39:29.665 +0000 UTC ±1s (in 23ms)
```

But if ping-version is set to `IETF-Roughtime` (as it it in [ecosystem.json](https://github.com/cloudflare/roughtime/blob/master/ecosystem.json)), then it fails:

```
$ go run cmd/getroughtime/main.go -ping roughtime.cloudflare.com:2003 -pubkey 0GD7c3yP8xEc4Zl2zeuN2SlLvDVVocjsPSL8/Rl/7zg= -ping-version IETF-Roughtime
Ping error: protocol: response is missing NONC tag
exit status 1
```