[deps] Update mock-ssh-server requirement from ~=0.8.0 to ~=0.9.1

Updates the requirements on [mock-ssh-server](https://github.com/carletes/mock-ssh-server) to permit the latest version.
- [Release notes](https://github.com/carletes/mock-ssh-server/releases)
- [Commits](carletes/mock-ssh-server@0.8.0...0.9.1)

---
updated-dependencies:
- dependency-name: mock-ssh-server
  dependency-type: direct:production
...

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

requirements-test.txt

@@ -1,4 +1,4 @@
 openwisp-utils[qa,selenium] @ https://github.com/openwisp/openwisp-utils/tarball/master
 django-redis~=5.2.0
-mock-ssh-server~=0.8.0
+mock-ssh-server~=0.9.1
 responses~=0.23.1