Reproduction steps:
1. Open the attached project “ImporterBug”
2. In the Project window select “Assets/justcube” fbx file
3. Inspect the Console and Inspector windows
Expected result: The Inspector is using the custom Asset Importer
Actual result: There are errors thrown in the Console window “The previous instance of Editor.CustomModelImporterEditor has not been disposed correctly”
Reproducible with: 2020.3.46f1, 2021.3.21f1, 2022.2.11f1, 2023.1.0b8, 2023.2.0a6
Reproducible on: macOS 13.1 (Intel), Windows 10