[6.5.x] fix: log constraint violation errors correctly

[Michel (cyl3x)]

1. Why is this change necessary?

Constraint violation errors were not logged correctly, as the json-seralized exception does not contain any information about the reasons for the violations - just the amount of them

2. What does this change do, exactly?

Serializes the constraint violation list correctly

3. Describe each step to reproduce the issue or behaviour.

-

4. Please link to the relevant issues (if any).

• relates fix: log constraint violation errors correctly #550

5. Checklist

• I have written tests and verified that they fail without my change
• I have created an entry in the CHANGELOG.md files with all necessary user information about my changes
• This change has comments for package types, values, functions, and non-obvious lines of code
• I have read the contribution requirements and fulfill them.