Fix flake8 and check-manifest Followup fa292e9

Merge 3.26 This fixes tests with psycopg2

DeprecationWarning: In future versions of Waitress clear_untrusted_proxy_headers will be set to True by default. You may opt-out by setting this value to False, or opt-in explicitly by setting this to True. Source: https://docs.pylonsproject.org/projects/waitress/en/stable/arguments.html?highlight=clear_untrusted_proxy_headers > This tells Waitress to remove any untrusted proxy headers ("Forwarded", > "X-Forwared-For", "X-Forwarded-By", "X-Forwarded-Host", "X-Forwarded-Port", > "X-Forwarded-Proto") not explicitly allowed by trusted_proxy_headers. According to grep we don't use any of those headers so let's turn it on for security reasons.