Bump djangorestframework from 3.14.0 to 3.15.2 in /src/backend (#7520)

* Bump djangorestframework from 3.14.0 to 3.15.2 in /src/backend

Bumps [djangorestframework](https://github.com/encode/django-rest-framework) from 3.14.0 to 3.15.2.
- [Release notes](https://github.com/encode/django-rest-framework/releases)
- [Commits](https://github.com/encode/django-rest-framework/compare/3.14.0...3.15.2)

---
updated-dependencies:
- dependency-name: djangorestframework
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

* fix req

* fix deps again

* patch serializer

* bump api version

* Fix "min_value" for DRF decimal fields

* Add default serializer values for 'IPN' and 'revision'

* Add specific serializer for email field

* Bump API version

* code cleanup

* fix tests

* allow null for email too

* fix formatting

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Matthias Mair <code@mjmair.com>
Co-authored-by: Oliver Walters <oliver.henry.walters@gmail.com>

src/backend/InvenTree/company/serializers.py

@@ -166,6 +166,10 @@ class CompanySerializer(
 
     image = InvenTreeImageSerializerField(required=False, allow_null=True)
 
+    email = serializers.EmailField(
+        required=False, default='', allow_blank=True, allow_null=True
+    )
+
     parts_supplied = serializers.IntegerField(read_only=True)
     parts_manufactured = serializers.IntegerField(read_only=True)
     address_count = serializers.IntegerField(read_only=True)