Drop support for and remove references to EOL Python 3.6 (#11683)

* 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

.github/workflows/tests.yml

@@ -141,7 +141,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - name: Test with old deps
-        uses: docker://ubuntu:bionic # For old python and sqlite
+        uses: docker://ubuntu:focal # For old python and sqlite
         with:
           workdir: /github/workspace
           entrypoint: .ci/scripts/test_old_deps.sh
@@ -213,15 +213,15 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - sytest-tag: bionic
+          - sytest-tag: focal
 
-          - sytest-tag: bionic
+          - sytest-tag: focal
             postgres: postgres
 
           - sytest-tag: testing
             postgres: postgres
 
-          - sytest-tag: bionic
+          - sytest-tag: focal
             postgres: multi-postgres
             workers: workers
 

.github/workflows/twisted_trunk.yml

@@ -25,7 +25,7 @@ jobs:
       - run: sudo apt-get -qq install xmlsec1
       - uses: actions/setup-python@v2
         with:
-          python-version: 3.6
+          python-version: 3.7
       - run: .ci/patch_for_twisted_trunk.sh
       - run: pip install tox
       - run: tox -e py