collab: Make `admin` column non-nullable on `users` table (#36307)

Marshall Bowers created

This PR updates the `admin` column on the `users` table to be
non-nullable.

We were already treating it like this in practice.

All rows in the production database already have a value for the `admin`
column.

Release Notes:

- N/A

Change summary

crates/collab/migrations/20250816124707_make_admin_required_on_users.sql | 2 
1 file changed, 2 insertions(+)

Detailed changes