[Bug]: ERROR! Failed to install app '222860' (Invalid platform)

### User story

I want to run L4D2 server through LinuxGSM.

### Game

Left 4 Dead 2

### Linux distro

Debian 12

### Command

command: install

### Further information

Hi.
I've used to run l4d2 instances on other Debian 12 machines with LinuxGSM many times, but now I'm not allowed to run it anymore, not even running it manually with steamcmd

LinuxGSM output:
`Connecting anonymously to Steam Public...OK
Waiting for client config...OK
Waiting for user info...OK
ERROR! Failed to install app '222860' (Invalid platform)
Error! Installing l4d2server: SteamCMD: Unknown error occured
Please provide content log to LinuxGSM developers https://linuxgsm.com/steamcmd-errorRedirecting stderr to '/home/l4d2srv/.local/share/Steam/logs/stderr.txt'
Logging directory: '/home/l4d2srv/.local/share/Steam/logs'
[ 0%] Checking for available updates...
[----] Verifying installation...
UpdateUI: skip show logoSteam Console Client (c) Valve Corporation - version 1737515347
-- type 'quit' to exit --
Loading Steam API...OK`

Manual run output:
`Steam>app_update 222860 validate
ERROR! Failed to install app '222860' (Invalid platform)`

All dependencies are installed.
Kernel info: Linux Debian-1207-bookworm-amd64-base 6.1.0-30-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.124-1 (2025-01-12) x86_64 GNU/Linux

### Relevant log output

```shell

```

### Steps to reproduce

1. adduser l4d2server
2. su - l4d2server
3. curl -Lo linuxgsm.sh https://linuxgsm.sh && chmod +x linuxgsm.sh && bash linuxgsm.sh l4d2server
4. ./l4d2server install