File file_types restricts the type of file uploaded but can be overridden

[ecocarlisle]

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Is your feature request related to a problem? Please describe.
When I set the file_types=['.md'] the dropdown filters out all other file types. However, when uploading a file you can change the dropdown to include all files and this then allows you to upload any file type.

Describe the solution you'd like
I'd like the file object to only allow the file type identified in the list of file_types. User should not be able to switch to all file types as work around.

Additional context
No additional context.