App icon not working on GNOME/Wayland

**Describe the bug**
I set the app's icon but it shows as the default GNOME app icon.

**To Reproduce**
Here's the steps that I used:
```Rust
let icon = image::load_from_memory(include_bytes!("../res/icon.png")).unwrap();
let icon = egui::IconData {
width: icon.width(),
height: icon.height(),
rgba: icon.into_rgba8().into_raw(),
};

let viewport = egui::ViewportBuilder::default()
.with_icon(icon);

let native = eframe::NativeOptions {
viewport,
..Default::default()
};
```

**Expected behavior**
The correct icon is shown for the app.

**Screenshots**

**Desktop (please complete the following information):**
Hardware Information:
- Hardware Model: ASUS PRIME B550-PLUS
- Memory: 32.0 GiB
- Processor: AMD Ryzen™ 9 3900X × 24
- Graphics: AMD Radeon™ RX 7800 XT
- Disk Capacity: 2.0 TB

Software Information:
- Firmware Version: 3405
- OS Name: Fedora Linux 39 (Workstation Edition)
- OS Build: (null)
- OS Type: 64-bit
- GNOME Version: 45.3
- Windowing System: Wayland
- Kernel Version: Linux 6.7.3-200.fc39.x86_64

Start by tracing the eframe NativeOptions viewport and ViewportBuilder::with_icon path shown in the report, focusing on native Linux behavior under GNOME/Wayland. Reproduce the example on Fedora or another Wayland session and compare the configured icon with the icon displayed by GNOME; done means the supplied icon is shown instead of the default.

Written by the indexing model from the issue text.