fix(auth): record last sign-in on reverse proxy login (#38672)

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>

services/auth/reverseproxy.go

@@ -121,7 +121,7 @@ func (r *ReverseProxy) Verify(req *http.Request, w http.ResponseWriter, store Da
 	if r.CreateSession && sess != nil {
 		sessionUID, ok := sess.Get(session.KeyUID).(int64)
 		if !ok || sessionUID != user.ID {
-			handleSignIn(w, req, sess, user)
+			handleSignInNonInteractive(w, req, sess, user)
 		}
 	}
 	store.GetData()["IsReverseProxy"] = true