clientupdate: abort if current version is newer than latest (#9733)

This is only relevant for unstable releases and local builds. When local
version is newer than upstream, abort release.

Also, re-add missing newlines in output that were missed in
https://github.com/tailscale/tailscale/pull/9694.

Updates #cleanup

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

cmd/tailscale/cli/update.go

@@ -63,7 +63,7 @@ func runUpdate(ctx context.Context, args []string) error {
 	err := clientupdate.Update(clientupdate.Arguments{
 		Version:  ver,
 		AppStore: updateArgs.appStore,
-		Logf:     printf,
+		Logf:     func(f string, a ...any) { printf(f+"\n", a...) },
 		Stdout:   Stdout,
 		Stderr:   Stderr,
 		Confirm:  confirmUpdate,