Version upgrade/downgrade confirmation dialog buttons misaligned

[romlok]

Godot version

v4.1.stable.official [9704596] < Steam

System information

Godot v4.1.stable - Debian GNU/Linux trixie/sid trixie - Vulkan (Mobile) - dedicated NVIDIA GeForce GTX 1060 (nvidia) - Intel(R) Core(TM) i5-8400 CPU @ 2.80GHz (6 Threads)

Issue description

After Godot got upgraded 4.0 -> 4.1, when opening a project from the earlier version, I noticed that the buttons in the confirmation dialog look a bit squiffy:

(Somewhat aside, but that dialog should probably be able to deduce and be more precise about whether it's an upgrade or downgrade!)

Steps to reproduce

1. Have a project from Godot 4.0
2. Upgrade Godot to 4.1
3. Open project manager

Alternatively:

1. Create a new project in 4.1
2. Quit Godot
3. Edit the project.godot's config/features to read 4.0 instead of 4.1
4. Open project manager

Minimal reproduction project

default.zip

[Calinou]

Note that the button offset is swapped around on Windows, as evidenced in the screenshot present in godotengine/godot-proposals#7254.

[kleonc]

Same issue as in #50192 (comment). Such custom added button is being hidden:

godot/editor/project_manager.cpp

Line 2257 in 7030ac5

full_convert_button->hide();

but the spacer remains visible.