Conflict between the holiday request application and the filemanager application

To reproduce:

• install filemanager application (2.0.6) on an XWiki (7.4.2)
• go in the extensions UI, search for the holiday request application
• you will find that the extension manager says that version 2.0.6 is already installed, and will propose you to downgrade to 1.3.2

This is not normal, and it's due to an ID conflict between filemanager and holiday request.