Bump django-extensions from 3.0.6 to 3.0.8 in /cvat/requirements (#2144)

Bumps [django-extensions](https://github.com/django-extensions/django-extensions) from 3.0.6 to 3.0.8.
- [Release notes](https://github.com/django-extensions/django-extensions/releases)
- [Changelog](https://github.com/django-extensions/django-extensions/blob/master/CHANGELOG.md)
- [Commits](https://github.com/django-extensions/django-extensions/compare/3.0.6...3.0.8)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

cvat/requirements/development.txt

@@ -8,6 +8,6 @@ pylint-django==2.3.0
 pylint-plugin-utils==0.6
 rope==0.17.0
 wrapt==1.12.1
-django-extensions==3.0.6
+django-extensions==3.0.8
 Werkzeug==1.0.1
 snakeviz==2.1.0