UpdateAttribute erases an attribute's expiration date.

## Summary of Bug If an attribute has an expiration date, and `UpdateAttribute` is called on it, it will erase the expiration date in the attribute record (but keep expiration queue entry). ## Proposal Fix `UpdateAttribute` to properly look up and persist the existing expiration date to the updated version. ____ ## For Admin Use - [ ] Not duplicate issue - [ ] Appropriate labels applied - [ ] Appropriate contributors tagged - [ ] Contributor assigned/self-assigned