Description Incorrect resizing of toolbar when resizing window

To Reproduce

Select some tool with many options in toolbar (such as Line/Curve)
Make window somewhat smaller
Observe the toolbar is messed up (almost out of visible area)

Additional Info <img width="715" height="188" alt="Image" src="https://github.com/user-attachments/assets/5ab27c2a-e1ea-4440-96d5-a5a8d0c35037" />

https://github.com/user-attachments/assets/65d5744b-ae00-47d7-a35d-7dc4aa26db65

Version Pinta 3.1.1, Linux Mint Cinnamon 22.2

Incorrect resizing of toolbar when resizing window when overlay scrollbars are disabled

Issue Description