Date attrs set after creation in report import

A Pro dev needs to check this.

https://jira.tor.rapid7.com/browse/MSP-11021

## Steps to verify
- [ ] Be on pro staging branch
- [ ] Start foreman
- [ ] Generate some data: `rails runner db/runners/generate_dataset.rb --host-count=7`
- [ ] In LoadTesting workspace, generate an Audit report (more is fine, just need at least one report generated)
- [ ] Exports -> Export Data, generate a Zip Workspace export of LoadTesting
- [ ] In a new workspace, import the zip workspace export created
- [ ] Verify no errors in import task
- [ ] Once complete, you should have hosts and such that you exported
- [ ] Reports -> Show Reports, exported reports should show up here. Click on the single view to verify the artifact loads as well.