[BUG] OAI Custom stylsheet can not be uploaded

[beatrycze-volk]

Description

In the plugin configuration the stylesheet can not be added:

Reproduction

Steps to reproduce the behaviour:

1. Go to configuration page
2. Click on Select & upload files
3. Choose file
4. See error

Expected Behavior

It should be spossible to upload custom stylesheets.

Screenshots and Examples

Environment

• TYPO3 version: 12.4.40
• PHP version: 8.2