Bump django from 2.2.4 to 2.2.28

Bumps [django](https://github.com/django/django) from 2.2.4 to 2.2.28.
- [Release notes](https://github.com/django/django/releases)
- [Commits](https://github.com/django/django/compare/2.2.4...2.2.28)

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

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

requirements.txt

@@ -35,7 +35,7 @@ daphne==2.3.0
 decorator==4.3.0
 defusedxml==0.6.0
 dill==0.2.9
-Django==2.2.4
+Django==2.2.28
 django-bootstrap3==11.0.0
 django-bootstrap4==0.0.7
 django-celery-beat==1.4.0