[deps] Update channels requirement from ~=3.0.2 to ~=4.2.0

Updates the requirements on [channels](https://github.com/django/channels) to permit the latest version.
- [Changelog](https://github.com/django/channels/blob/main/CHANGELOG.txt)
- [Commits](django/channels@3.0.2...4.2.0)

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

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

Author: dependabot[bot]

requirements.txt

@@ -1,5 +1,5 @@
 django-notifications-hq~=1.8.3
-channels~=3.0.2
+channels~=4.2.0
 openwisp-users~=1.1.0
 openwisp-utils[rest,celery]~=1.1.1
 markdown~=3.7.0