[deps] Update django-cors-headers requirement in /images/openwisp_base

Updates the requirements on [django-cors-headers](https://github.com/adamchainz/django-cors-headers) to permit the latest version.
- [Changelog](https://github.com/adamchainz/django-cors-headers/blob/main/CHANGELOG.rst)
- [Commits](adamchainz/django-cors-headers@4.4.0...4.6.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

images/openwisp_base/requirements.txt

@@ -4,7 +4,7 @@ django-redis
 psycopg2
 sentry-sdk
 supervisor~=4.2  # allows 4.x and > 4.2
-django-cors-headers~=4.4
+django-cors-headers~=4.6
 django-pipeline~=3.1
 uwsgi~=2.0.27
 django-celery-email~=3.0.0