Knowledge Base Dashboard subscriptions cannot be modified #1509

Describe the bug
A user has mentioned in https://bugzilla.mozilla.org/show_bug.cgi?id=1859181 that the subscribe panel from the Knowledge Base Dashboard page is broken (notification settings cannot be updated)

Preconditions
Sign in to SUMO.

Steps to reproduce
Steps to reproduce the behavior:

1. Go to https://support.allizom.org/en-US/contributors
2. Click on the "Subscribe" button.
3. Check or uncheck the boxes.
4. Refresh the page and click on the "Subscribe" button again.

Expected behavior
The checkboxes can be successfully modified (once checked they can be unchecked again). And after refreshing the SUMO page and accessing the "Subscribe" panel again, the previously checked checkboxes status should be saved and displayed accordingly.

Actual behavior
Once the checkoxes are checked they cannot be unchecked (they become greyed out).
If the user checks a checkbox, refreshes the page and clicks on the "Subscribe" button it can be noticed that the previously checked checkboxes are not displayed as checked.

Screencasts

Desktop:

• OS: Window 10
• Browser: Firefox

Additional context
Reproducible on both stage and prod