ci(lint): bump Python to 3.13 and fix Ruff C420

- Bump Python version in GitHub Actions matrix from 3.12 to 3.13
- Adjust Ruff rule C420 (redundant return in generator) to prevent false positives

Author: RandomProgramm3r

.github/workflows/linting.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.12"]
+        python-version: ["3.13"]
     steps:
       - name: Checkout repository
         uses: actions/checkout@v3

promo_code/user/validators.py

@@ -82,7 +82,7 @@ def __call__(self, value):
 
         if missing_fields:
             raise rest_framework.serializers.ValidationError(
-                {field: 'This field is required.' for field in missing_fields},
+                dict.fromkeys(missing_fields, 'This field is required.'),
             )
 
         serializer = self.__class__(data=value)