Reproduction steps:
1. Open the attached “BugRepro” project
2. Open the “Scenes/SampleScene” Scene
3. Select the “Rigidbody other” GO in the Hierarchy window
4. Observe the “Fixed Joint” component in the Inspector window
5. Enter the Play Mode
6. Observe both the Console and Inspector windows

Expected result: The “Connected Articulation Body” value is removed
Actual result: Error is printed out: “A joint can't connect the body to itself.”

Reproducible with: 2021.3.36f1, 2022.3.22f1, 2023.2.15f1, 6000.0.0b12

Reproducible on: Windows 10, Ubuntu 22.04
Not reproducible on: No other environment tested