Campaign contact "updated_at" not updated when reassigning contacts

[sjwmoveon]

Describe the bug
When reassigning contacts, the updated_at value in the campaign_contacts table remains unchanged.

To Reproduce
Steps to reproduce the behavior:

1. Go to [base_url]/admin/[campaign_id]/incoming for a campaign with active contacts.
2. Select some messages and under "message actions", "reassign selected" or "reassign all N matching" to reassign the messages to a different user.
3. In SQL, select * from campaign_contacts order by updated_at desc; (or use a more specific query)
4. Note that the recently reassigned contacts do not have a new updated_at value.

Expected behavior
When a campaign_contact is updated, its updated_at value should change.

Platform (please complete the following information):

• OS: MacOS 14.3.1 (23D60)
• Browser Firefox 25.0.3
• Desktop or Mobile? Desktop
• Version [e.g. 22] 13.1.0