Which Umbraco version are you using?

17.0.0-RC4

Bug summary

Found by @NillasKA

This also occurs on 16.4.0-RC. Apparently, I'm allowed to insert files from the root project folder and not just wwwroot as a thumbnail. This then allows me to insert files with the file type cs, csproj, JSON and so on. See GIF for clarification

The issue was not present in 16.0.0

Specifics

Steps to reproduce

1. Install Umbraco project from the template
2. Create an element type
3. Create a data type with a block
4. Try to add a thumbnail
5. See the project root folder being opened at the root project folder

Expected result / actual result

Expected: I would expect that it as only able to upload images, and that the wwwroot folder was opened

Actual: Able to upload pretty much everything. And the project folder is opened

This item has been added to our backlog AB#62658