[Groupings] Content is not saved

[MalwareCantFly]

Description

Groupings -> Content:
Adding content and hiting the save button, doesn't do anything.

Environment

Demo environement

Reproducible Steps

Steps to create the smallest reproducible scenario:

1. Go to a specific grouping
2. Click the Content tab
3. Edit the content and hit the save button
4. Exit the content tab, and come back to it
5. There is no content

Expected Output

Content should be saved :)

Thanks!

[labo-flg]

Cannot edit the main content + adding files fail too.

[Kedae]

Linked to #6379