Script Component is treated as an Editor script when attaching to GameObject and when there are two partial classes with the same name and file name in the project

Reproduction steps:
1. Open the attached "repro_IN-36142WrongMessage.zip" project
2. Open the "Assets/Scenes/SampleScene" Scene
3. In the Hierarchy window, select the "TestObject" GameObject
4. In the Project window, drag and drop the "Assets/FirstPartClass" script to the Inspector window
5. Observe the error message

Expected result: The error message shows "Can't add script component 'FirstPartClass' because the script class cannot be found..."
Actual result: The error message shows "The script is an editor script."

Reproducible with: 2022.2.9f1, 2022.2.13f1, 2023.1.0b10, 2023.2.0a8
Not reproducible with: 2022.2.8f1
Could not test with: 2020.2.46f1, 2021.3.22f1 (There is no error message)

Reproduced on: Windows 10