V3.5.1 to V4Beta2 conversion process deletes bezier curves (and malforms other keys) in animationplayers

[Proggle]

Godot version

v3.5.stable.official [991bb6ac7], v4.0.beta2.official [f8745f2f7]

System information

Windows 10

Issue description

When converting from Godot 3 to Godot 4 Beta 2, it appears that the Bezier curves in animation players get deleted. Sometimes this also results in producing this error message when Godot was expecting the curves to exist.

E 0:00:01:0137 _set: Condition "!d.has("handle_modes")" is true. Returning: false <C++ Source> scene/resources/animation.cpp:319 @ _set()

Steps to reproduce

Make an animation player in V3.5.1. Have a bezier curve in that player. Automatically convert the project into Godot 4 Beta 2.

Minimal reproduction project

Here's a minimal godot 3 project, and the broken converted version.

BezierFadeConversionBug.zip