The Editor Theme is changed only when The Editor is refocused

How to reproduce:

1. Create a new project
2. Go to the Preferences window
3. Select the “General“ section
4. Change the Editor Theme to “Light“
5. Observe the Editor

Expected results: The Editor changes the Editor Theme instantly
Actual results: The Editor changes the Editor Theme only when the Editor is refocused

Reproducible in: 2023.3.0b1
Not reproducible in: 2021.3.33f1, 2022.3.16f1, 2023.2.4f1, 2023.3.0a19

Reproduced on: Windows 11 Pro
Not reproduced on: macOS (M1, 2020) 13.5.2

Note: After restarting the Editor, the theme will not have changed.

Workaround: Focus on another application and refocus back to the Unity Editor to change the theme