Improve handling edge-cases in airlfow.models by applying mypy

[ashb]

And to fix these, I needed to fix a few other mistakes that are
used/called by DAG's methods.

Relates to #19891 - it doesn't completely fix any packages, but this change was getting larger.

/cc @khalidmammadov

[potiuk]

AH NOOO!!!!!! I MISSED THE #20000 one! Bummer!

[uranusjr]

It’s probably because Pendulum invents its own timezone class (which is fine) and expects to only receive that timezone class in its own datetime class (which is not fine). I’ll take a look.

[uranusjr]

For other reviewers wondering, this method returns a command list (for e.g. subprocess), and passing in a None would not work, so all existing usages of this function should already be passing in a run_id, making this change safe.

[github-actions]

The PR most likely needs to run full matrix of tests because it modifies parts of the core of Airflow. However, committers might decide to merge it quickly and take the risk. If they don't merge it quickly - please rebase it to the latest main at your convenience, or amend the last commit of the PR, and push it with --force-with-lease.

[ashb]

I might need to merge #20079 first -- this is crashing in building docs for some reason.

[ashb]

This is what is causing the docs build to fail.

[ashb]

I have a fix for it -- so we can merge this and spend a bit more time looking at the sphinx upgrade.

[ashb]

Conflict is only in the import section:

<<<<<<< models-typing-partial
from airflow.utils.session import NEW_SESSION, create_session, provide_session
=======
from airflow.utils.retries import run_with_db_retries
from airflow.utils.session import create_session, provide_session
>>>>>>> main

so once these tests pass I'll fix conflict then merge without waiting for another test run.

[ashb]

Green build https://github.com/apache/airflow/actions/runs/1549766290 -- rebasing + merging.