Update django requirement from <3,>=2.2.12 to >=2.2.12,<4

Updates the requirements on [django](https://github.com/django/django) to permit the latest version.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@2.2.12...3.0.6)

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

test_reqs.txt

@@ -1,4 +1,4 @@
-Django>=2.2.12,<3
+Django>=2.2.12,<4
 Markdown==3.2.2
 coverage==5.1
 flake8==3.8.1