Resolve "Error when uploading a few designs in a row"

What does this MR do?

This MR fixes an issue with uploading multiple designs. Previously, they could have a non-unique ID equal to null. With the fix designs always have unique IDs.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Related issues

#34320 (closed)