Bug in get_api_key_info

Debbuged and found an issue why I cant test my api key.

With headscale v0.25.1 seems like it returns first 7 chars.

In get_api_key_info your code:
```py
key_prefix = str(api_key[0:10])
```

Please, check different versions of headscale or use another checking mehtod

Working version:

```py
key_prefix = str(api_key[0:7])
```