Device registration does not work in `0.7.0-beta.2`

[cheetah747]

Description

1. Click add device button,
2. Click the Register Machine Key
3. Select the Owner just like "lain"（the user "lain" is an Unlinked Headscale Users）
4. Click confirm and then it jump to an error page like this picture:
   （But if I use the headscale's command like headscale nodes register --key XXXXXXXXXXXXXXX --user lain ,it will be added successfully.）

Headplane Version

v0.7.0-beta.2

Headscale Version

v0.28.0

[linear]

HP-530

[paperluigis]

this action sends a payload like action_id=register&register_key=aaaaaaaaaaaaaaaaaaaaaaaa&user=1 (with numeric identifier) while headscale expects action_id=register&register_key=aaaaaaaaaaaaaaaaaaaaaaaa&user=lain (with username)