Seamless looping animations stutter at the last frame before looping when using AnimationTree

### Tested versions

Godot 4.2.2 stable

### System information

11th Gen Intel(R) Core(TM) i5-11400H @ 2.70GHz RTX 3050 laptop 16 gb ram Windows 10 64bit

### Issue description

https://github.com/godotengine/godot/assets/170141752/d2ed8aeb-c9f2-42b4-83df-d0bcac505e94

the animation works noramlly when not using blend or add nodes or when animated in animmator individually

### Steps to reproduce

make looping animation, try blending or adding two of them.

### Minimal reproduction project (MRP)

dont have

Start by reproducing the issue with a looping animation blended or added through AnimationTree, then compare it with the standalone animation behavior described in the report. A minimal reproduction project is needed because none is provided. Done means the loop no longer stutters in the blended or additive setup.

Written by the indexing model from the issue text.