Surfshark DNS can't be added as custom server

### Please answer the following questions for yourself before submitting an issue

- [x] Filters were updated before reproducing an issue
- [x] I checked the [knowledge base](https://adguard.com/kb/) and found no answer
- [x] I checked to make sure that this issue has not already been filed

### AdGuard version

4.5.21

### Environment

- OS: 26.6
- Device: iOS

### Ad Blocking

_No response_

### Privacy

_No response_

### Social

_No response_

### Annoyances

_No response_

### Security

_No response_

### Other

_No response_

### Language-specific

_No response_

### Advanced protection for Safari

- [ ] yes, I do

### Which DNS server do you use?

Custom DNS

### DNS protocol

DNS-over-HTTPS

### Custom DNS

https://dns.surfsharkdns.com/dns-query

### DNS filtering

- [ ] yes, I do

### Custom DNS filter

_No response_

### DNS implementation

AdGuard

### Tunnel mode

Split-Tunnel

### Low-level settings

Bootstrap server:
Fallback server:
Blocking mode, etc:

### Issue Details

None of Surfshark DNS work as custom in AdGuard for iOS: https://adguard-dns.io/kb/general/dns-providers/#surfshark-dns

### Expected Behavior

_No response_

### Actual Behavior

Error: invalid upstream

### Screenshots

Screenshot 1

### Additional Information

_No response_