How to reproduce:
1. Create a new project
2. Create a new C# Script
3. Open the C# Script

Expected result: The newly created C# script derives from MonoBehaviour
Actual result: The newly created C# script derives from StateMachineBehaviour

Reproducible with: 2023.3.0a9
Not reproducible with: 2021.3.31f1, 2022.3.10f1, 2023.1.16f1, 2023.2.0b12, 2023.3.0a8

Reproduced on: macOS Ventura 13.5 (Intel), Windows 11 (User reported)
Not reproduced on: No other environment tested

Notes:
- The reporter has noted that - “Likely cause: Scripting submenu has Playables submenu under it with two items, likely there should be three there (another for mentioned state machine).”
- The same happens if using C# Script from the Scripting submenu.