[deps] Update responses requirement from ~=0.25.3 to ~=0.25.6

Updates the requirements on [responses](https://github.com/getsentry/responses) to permit the latest version.
- [Release notes](https://github.com/getsentry/responses/releases)
- [Changelog](https://github.com/getsentry/responses/blob/master/CHANGES)
- [Commits](getsentry/responses@0.25.3...0.25.6)

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

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

Author: dependabot[bot]

requirements-test.txt

@@ -5,5 +5,5 @@ openwisp-utils[qa,selenium] @ https://github.com/openwisp/openwisp-utils/tarball
 channels_redis~=4.2.1
 django_redis~=5.4.0
 mock-ssh-server~=0.9.1
-responses~=0.25.3
+responses~=0.25.6
 psycopg2-binary~=2.9.10