chore(deps): update dependency cryptography to v2.9.2 [(#3666)](GoogleCloudPlatform/python-docs-samples#3666)

Co-authored-by: Takashi Matsuo <tmatsuo@google.com>

Author: renovate-bot

samples/attestations/requirements.txt

@@ -1,2 +1,2 @@
-cryptography==2.8
+cryptography==2.9.2
 pem==20.1.0