Explicitly upgrade openssl in docker file and enforce new version of cryptography (#9697)

synapse/python_dependencies.py

@@ -82,6 +82,9 @@ REQUIREMENTS = [
     "Jinja2>=2.9",
     "bleach>=1.4.3",
     "typing-extensions>=3.7.4",
+    # We enforce that we have a `cryptography` version that bundles an `openssl`
+    # with the latest security patches.
+    "cryptography>=3.4.7;python_version>='3.6'",
 ]
 
 CONDITIONAL_REQUIREMENTS = {