Relational customfield causes other customfields to be nulled on partial update if omitted

[RoyalFoxy]

Describe the bug
Updating a customfield relation on a translateable entity with a partial update of other customfields results in the omitted fields being nulled.

To Reproduce
Steps to reproduce the behavior:

1. Create a customfield which is a relation or a list of relations to another entity on a translatable entity
2. Create another primitive customfield
3. Update the customfield relation and omit some other customfields
4. Check the output

Expected behavior
A partial update including a relation update should not null other omitted customfields

Environment (please complete the following information):

• @vendure/core version: 2.2.3
• Nodejs version: 21.0.0
• Database (mysql/postgres etc): postgres & sqlite

Additional context
Discord issue