Alt+Enter key combination bypasses pin screen

[solemgar]

Your system information

• Steam client version: Steam Deck Oled
• SteamOS version: Tested on Bazzite but certainly should be reproducible in SteamOS (can't test right now)
• Opted into Steam client beta?: N/A
• Opted into SteamOS beta?: N/A
• Have you checked for updates in Settings > System?: Yes

Please describe your issue in as much detail as possible:

When in the PIN Screen, pushing alt+enter in a physical keyboard closes gaming mode and sends you to the desktop version of the Steam application. There is not much that can be interacted with, but it is a potential security issue.

Steps for reproducing this issue:

1. Connect a physical keyboard
2. Trigger the PIN screen
3. Press alt+enter on the physical keyboard

Reported as well in ublue-os/bazzite#1945 (comment)