Add missing dependency on types-cryptography

For some reason it is not an issue within tox; but mypy has been
bugging me about this for a while.

requirements-test.txt

@@ -15,6 +15,7 @@ swh.loader.git >= 0.8.0
 swh-scheduler[testing] >= 0.5.0
 swh.storage >= 0.1.1
 types-chardet
+types-cryptography
 types-docutils
 types-psycopg2
 types-pyyaml