Do not delete latest snapshot when deleting unused snaphots

[midigofrank]

Describe the bug
When the latest snapshot of a workflow is attached to a work order and the work order is deleted during data retention, the snapshot is also deleted alongside it. When the latest snapshot is deleted, the workflow edit page becomes inaccessible.

Version number 2.10.16

I have reproduced this locally on main:

• Yes
• No

To Reproduce Steps to reproduce the behavior:

This is how it happens:

1. You have your latest workflow, say version 2
2. You create a work order with this version.
3. The retention period for the project is set to 5 days.
4. When the work order gets old enough, and the day arrives for retention. That work order gets deleted and the snapshot along side with it given there is no other work order referencing it.
5. Remember that the workflow is still set at version 2 . When you try viewing the workflow edit page, it will crash because it cannot find a snapshot for version 2