Reverse proxy and SSPI logins establish a session but never recorded
`last_login_unix`, so those users stayed "Never Signed-In" in admin.
The write is folded into the language update that `handleSignIn` already
does, so it stays at one query and only runs when a session is
established.
Fixes https://github.com/go-gitea/gitea/issues/7836
---------
Co-authored-by: roman s <roman.sukach@dust-labs.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
