[deps] Update redis requirement from ~=6.2.0 to ~=6.4.0

Updates the requirements on [redis](https://github.com/redis/redis-py) to permit the latest version.
- [Release notes](https://github.com/redis/redis-py/releases)
- [Changelog](https://github.com/redis/redis-py/blob/master/CHANGES)
- [Commits](redis/redis-py@v6.2.0...v6.4.0)

---
updated-dependencies:
- dependency-name: redis
  dependency-version: 6.4.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements-test.txt

@@ -4,5 +4,5 @@ freezegun~=1.5.4
 openwisp-monitoring @ https://github.com/openwisp/openwisp-monitoring/tarball/1.2
 openwisp-controller @ https://github.com/openwisp/openwisp-controller/tarball/1.2
 openwisp-utils[qa,selenium,channels-test] @ https://github.com/openwisp/openwisp-utils/tarball/1.2
-redis~=6.2.0
+redis~=6.4.0
 django_redis~=6.0.0