chore(python): drop python 3.6 (#420)

Source-Link: googleapis/synthtool@4f89b13
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:e7bb19d47c13839fe8c147e50e02e8b6cf5da8edd1af8b82208cd6f66cc2829c

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>
Co-authored-by: nicain <nicholascain@google.com>

Author: gcf-owl-bot[bot]

Dialogflow-CX/noxfile.py

@@ -89,7 +89,7 @@ def get_pytest_env_vars() -> Dict[str, str]:
 
 # DO NOT EDIT - automatically generated.
 # All versions used to test samples.
-ALL_VERSIONS = ["3.6", "3.7", "3.8", "3.9", "3.10"]
+ALL_VERSIONS = ["3.7", "3.8", "3.9", "3.10"]
 
 # Any default versions that should be ignored.
 IGNORED_VERSIONS = TEST_CONFIG["ignored_versions"]