Captive portal checks report true on some airlines with a squid intermediary

```
% time curl -I http://derp10d.tailscale.com/generate_204
HTTP/1.1 204 No Content
Date: Fri, 31 Jan 2025 20:44:39 GMT
Server: PAC Web Server
Cache-Control:
X-Content-Type-Options: nosniff
X-XSS-Protection: 1; mode=block
Strict-Transport-Security: max-age=31536000; includeSubdomains; preload
Allow: GET, POST, HEAD
X-Cache: MISS from bc01
Via: 1.1 bc01 (squid/3.5.27)
Connection: close
```

with parameter:

```
% time curl -I 'http://derp10d.tailscale.com/generate_204?v=2'
HTTP/1.1 204 No Content
Date: Fri, 31 Jan 2025 20:46:38 GMT
X-Cache: MISS from bc01
Via: 1.1 bc01 (squid/3.5.27)
Connection: close
```