Fixes #12458

Co-authored-by: Sean Quah <seanq@element.io>
Co-authored-by: Dan Callahan <danc@element.io>

* remove reference in comments to python3.6

* upgrade tox python env in script

* bump python version in example for completeness

* upgrade python version requirement in setup doc

* upgrade necessary python version in __init__.py

* upgrade python version in setup.py

* newsfragment

* drops refs to bionic and replace with focal

* bump refs to postgres 9.6 to 10

* fix hanging ci

* try installing tzdata first

* revert change made in b979f336

* ignore new random mypy error while debugging other error

* fix lint error for temporary workaround

* revert change to install list

* try passing env var

* export debian frontend var?

* move line and add comment

* bump pillow dependency

* bump lxml depenency

* install libjpeg-dev for pillow

* bump automat version to one compatible with py3.8

* add libwebp for pillow

* bump twisted trunk python version

* change suffix of newsfragment

* remove redundant python 3.7 checks

* lint

Instead of only dumping them if trial passes.

Setting `update_existing: true` in the `create-an-issue` GitHub Action
will avoid opening duplicate issues if an open issue already exists with
an identical title.

If no open issues match the title, then a new issue will be created.

This helps avoid spamming our issue tracker should there be a failure
when testing against Twisted's trunk.

This PR also pins the SHA of the `create-an-issue` action to mitigate
the risk of a malicious actor gaining access to JasonEtco's account.

See GitHub's page on security hardening third party actions for more:
https://docs.github.com/en/actions/learn-github-actions/security-hardening-for-github-actions#using-third-party-actions



Signed-off-by: Dan Callahan <danc@element.io>

This creates a GHA workflow which runs at 8am every day, and runs mypy, trial and sytest against Twisted's current trunk. If any of the jobs fail, it opens an issue.