Silk.NET.OpenGL.Extensions.ImGui: Key mod not sent to ImGui IO

# Summary
Key mods like Ctrl, Alt, Shift are not sent to ImGUI during `imguiController.Update((float)delta);`

# Steps to reproduce
Reproducible here: https://github.com/dotnet/Silk.NET/tree/main/examples/CSharp/OpenGL%20Demos
Windows 11, using `WindowOptions.Default`

1. Add `ImGui.ShowDemoWindow();` before `imguiController.Render();` to draw demo window
2. Start the project
3. In demo window, navigate to "Inputs & Focus" category
4. Press "Ctrl", "Ctrl+A", "Shift+Tab" or any other key combo with mod keys

**Expected**: Mods should appear in "Keys mods:" label. "Keys down:" label should show "ModCtrl", "ModShift", etc... together with "LeftCtrl", "LeftShift", etc...

**Actual**: Mods do not appear in "Keys mods:" label. "Keys down:" label contains only "LeftCtrl", "LeftShift", etc... This results in shortcuts not working at all. You can test shortcuts in "Shortcuts" subcategory of "Inputs & Focus"

# Comments
Issue is somewhere here https://github.com/dotnet/Silk.NET/blob/3c0313b2d69bbde12224c759a76bc2e7e064a893/src/OpenGL/Extensions/Silk.NET.OpenGL.Extensions.ImGui/ImGuiController.cs#L250