github workflow: Add python-3.8

[tsnoam]

No description provided.

[tsnoam]

• workflow fails on py3.8 linux. need to investigate
• workflow hangs on py3.8 windows. need to investigate as well.

[vergeev]

I also wanted to note that it fails on macOS Catalina with an error that basically reads

from telegram import Update
ImportError: cannot import name 'Update' from 'telegram' (unknown location)

Only with python 3.8.

[Bibo-Joshi]

GH Actions now provides py3.8 (actions/setup-python#30), but test_updater hangs on windows. Will need to investigate

[Bibo-Joshi]

GH Actions now provides py3.8 (actions/setup-python#30), but test_updater hangs on windows. Will need to investigate

Apparently urlopen() doesn't return for some reason. I remember having a similar problem in #1791, but the networking backend is beyond me 🙈

[Bibo-Joshi]

@Bibo-Joshi @tsnoam can you maybe have a look?

[Bibo-Joshi]

Found the issue at tornadoweb/tornado#2608 and a workaround here.

As far as I can see, urlopen is only used explicitly in test_updater (and in the vendored urllib3 …), so I guess we don't have to make changes elsewhere.

[tsnoam]

@Bibo-Joshi Good catch!!!

This is a problem related to the webhook Updater.
It's the only component using Tornado.

The workaround is good and should probably be applied in webhookhandler.py

We should also consider moving all imports of tornado to the init of the webhook instead of top of the file.

[Bibo-Joshi]

@tsnoam @tsnoam Added the workaround to WebhookHandler, but left the imports at the top of the file, since WebhookServer and WebhookAppClass in the same file use them, too.

[Bibo-Joshi]

CI fails:

• py3.7 is unrelated (set_game_score)
• codecov: Don't know how to get the coverage up …