[Bug]: Debian 13 is not using sources.list anymore

### Severity

severity: low

### Reproducibility

reproducible: always

### Regression

regression: no

### Affects latest release

latest-release: yes

### User story

As a Server Admin, I want the warning not to be displayed so that the console is not spammed by it.

### Script name

sfserver, pwserver, pmcserver, fcserver

### Game

Palworld, Paper Minecraft, Factorio, Satisfactory

### Linux distro

Other

### Command

command: update

### Expected behavior

The scripts read the proper source list location on Debian 13:

/etc/apt/sources.list.d/

### Actual behavior

If a update script or any other is run, the following output gets shown:

grep: /etc/apt/sources.list: No such file or directory

On Debian 13 the source lists are now found at: /etc/apt/sources.list.d/

### Further information

Is part of every update script

### Pre-checks

- [x] I ran update and validate before reporting this issue.

### Relevant log output

```shell
[ .... ] Starting sfserver: grep: /etc/apt/sources.list: No such file or directory
```

### Steps to reproduce

1. Install LGSM on a Debian 13 system
2. Start a script like: ./sfserver update
3. Read the output

Start with the update entry points in sfserver, pwserver, pmcserver, and fcserver, then search for the /etc/apt/sources.list reference that produces the reported grep warning. Run an update on Debian 13 to confirm the warning is gone and the scripts use /etc/apt/sources.list.d/.

Written by the indexing model from the issue text.