* Update relations.py
Currently if you define the slug field as a nested relationship in a `SlugRelatedField` while many=False, it will cause an attribute error. For example:
For this code:
```
class SomeSerializer(serializers.ModelSerializer):
some_field= serializers.SlugRelatedField(queryset=SomeClass.objects.all(), slug_field="foo__bar")
```
The POST request (or save operation) should work just fine, but if you use GET, then it will fail with Attribute error:
> AttributeError: 'SomeClass' object has no attribute 'foo__bar'
Thus I am handling nested relation here. Reference: https://stackoverflow.com/questions/75878103/drf-attributeerror-when-trying-to-creating-a-instance-with-slugrelatedfield-and/75882424#75882424
* Fixed test cases
* code comment changes related to slugrelatedfield
* changes based on pre-commit and removed comma which was added accidentally
* fixed primary keys of the mock object
* added more test cases based on review
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Co-authored-by: Arnab Shil <arnab.shil@thermofisher.com>