Only one category assignable

[tithrion]

Description
I can only assign one category to a recipe.
On selection of multiple categories, they are shown, but not saved when clicking on save.

Reproduction

1. Select a recipe
2. click on edit
3. select multiple categories
4. save
5. reopen the recipe
6. => all but the first category are lost

Expected behavior
Multiple categories can be assigned and saved.

Actual behavior
Only first category is saved.

Screenshots
If applicable, add screenshots to help explain your problem.

Browser
Firefox 147.0.4

Versions
Nextcloud server version: 32.0.6
Cookbook version: 0.11.6
Database system: MariaDB