Bump django in /examples/Python/python-django-webapp-sample (#1052)

Bumps [django](https://github.com/django/django) from 4.2.18 to 4.2.21.
- [Commits](django/django@4.2.18...4.2.21)

---
updated-dependencies:
- dependency-name: django
  dependency-version: 4.2.21
  dependency-type: direct:production
...

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Author: dependabot[bot]

examples/Python/python-django-webapp-sample/requirements.txt

@@ -1,4 +1,4 @@
-Django==4.2.18
+Django==4.2.21
 whitenoise==6.4.0
 azure-appconfiguration-provider==1.3.0
 azure-identity==1.16.1