Not available yet. Kizuna does not accept git over SSH.

Use HTTPS. Create a personal access token under Settings, Access tokens, with repo:write if you need to push (repo:read is enough to clone and fetch). When git asks for a password, paste the token. The username can be anything.

git clone https://kizuna.example.com/myadmin/hello.git
git push origin main

The same token works as Authorization: Bearer <token> and as POST /api/v1/user/tokens for creating further tokens.