Tailscale update not taking modernize-sources from debian 13 and up

### What is the issue?

Tailscale update command doesnt take into account tailscale.sources apt list, only old tailscale.list format.

### Steps to reproduce

tailscale update
This will update Tailscale from 1.94.1 to 1.94.2. Continue? [Y/n] y
open /etc/apt/sources.list.d/tailscale.list: no such file or directory
root@Proxmox:~# cat /etc/apt/sources.list.d/tailscale.sources
Types: deb
URIs: https://pkgs.tailscale.com/stable/debian/
Suites: trixie
Components: main
Signed-By: /usr/share/keyrings/tailscale-archive-keyring.gpg

### Are there any recent changes that introduced the issue?

_No response_

### OS

_No response_

### OS version

_No response_

### Tailscale version

_No response_

### Other software

_No response_

### Bug report

_No response_