404 error when clicking "create and add another" when assigning a contact

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NetBox version

v3.1-beta1

Python version

3.7

Steps to Reproduce

1. View a site
2. Click the "add contact" button
3. Select a contact and role
4. Click "create and add another"

Expected Behavior

The contact assignment is created and a new form is displayed.

Observed Behavior

The contact assignment is created, however the user is redirected to a 404 error, complaining that /tenancy/contact-assignments/add/ cannot be found. This is because the redirect does not include the required object type and ID as URL parameters.

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Similar to #7741

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This also affects FHRP group assignment.