Animation editor wraps the `Fit to panel` button too early when tweaking layout

### Tested versions

- Reproducible in: 4.6dev3, 4.5.1stable

### System information

Godot v4.6.dev3 - Windows 10 (build 19045) - Multi-window, 1 monitor - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 4070 (NVIDIA; 32.0.15.7628) - 12th Gen Intel(R) Core(TM) i5-12490F (12 threads) - 31.81 GiB memory

### Issue description

When expanding the scene and inspector panels on both sides of the editor, animation editor wraps the `Fit to panel` button too early.

Screenshot:

Demo:

https://github.com/user-attachments/assets/06b046d1-6b3e-4903-89e8-f6966bd48ecb

### Steps to reproduce

N/A

### Minimal reproduction project (MRP)

N/A

No file, test, or reproduction steps are named. Reproduce the layout in the animation editor by expanding the scene and inspector panels on both sides, then trace the animation editor controls responsible for the Fit to panel button. Done means the button does not wrap prematurely in this layout.

Written by the indexing model from the issue text.