Changing Animation Key Bezier Handles throws error

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Tested versions

Reproducible in both 4.2.1 and 4.3.dev [9adb7c7]

System information

Windows 10

Issue description

Changing the Handle Mode of a Key in the Bezier Animation Editor via the Inspector throws the following error:
core/object/undo_redo.cpp:345 - Error calling UndoRedo method operation '_bezier_track_set_key_handle_mode': 'AnimationTrackKeyEdit::_bezier_track_set_key_handle_mode': Instance is null

Changing Handle Mode via Right-Click Context Menu throws the following error (twice):
UndoRedo history mismatch: expected 0, got 4.

The errors seem to appear independent of whether the keys have been added via AnimationBezierEditor or via the normal AnimationEditor.

Steps to reproduce

1. Have a scene with an animation player and add a bezier track to it
2. Add Keyframes
3. Change the handle mode of these keyframes (either via Right-Click context menu or via the inspector)
4. Observe errors

Minimal reproduction project (MRP)

AnimationTestProject.zip

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Seems to be related to #73603, #74088, and #65539.