[Bug]: Game doesn't react to Gamepad events

[NuclearNemo]

SuperTux Version

0.6.3-1606-g3af6b30f2 nightly appimage

System Information

Kubuntu 25.04, Fedora 41 KDE, both amd64

Expected Behavior

Gamepad can be used to play Supertux.

Actual Behavior

Supertux doesn't react to Gamepad events.
When choosing "Manual configuration" in Joystick settings, buttons pressed on the Gamepad get recognized, but actually using them in the game or game menus doesn't work.

Steps To Reproduce Actual Behavior

1. Start Supertux nightly appimage.
2. Try to use the Gamepad.

Additional Information

My Gamepad:
Bus 001 Device 009: ID 2dc8:6006 8BitDo 8BitDo Pro 2

Gamepad works fine in Supertux stable 0.6.3-3 shipped by (K)Ubuntu 25.04.

Reproduced both on on Kubuntu 25.04 (kernel version: 6.12.0-16-generic) and Fedora 41 KDE (kernel version: 6.13.5-200).
Switching between Plasma Wayland and X11 session made no difference.

Guidelines For Reporting Issues

• I have read https://github.com/SuperTux/supertux/blob/master/CONTRIBUTING.md#bug-reports.
• I have verified this isn't an issue that's already been reported.
• I have verified this isn't a discussion, or an issue about a crash or a feature request, but rather an actual bug ─ that is, the game did something not intended.
• I have verified this issue is not about wrong translations (use Transifex for those), or anything unsupported (e.g. third-party add-ons).
• In this report, I have only included details about one (1) bug.
• If I make a mistake while submitting this report, I agree to use the "Edit" feature to correct it, instead of closing this issue and opening a new one.