With alpha2 without using the constraints https://github.com/apache/airflow/blob/constraints-master/constraints-3.6.txt , when accessing Webserver it fails with

```
Something bad has happened.
Please consider letting us know by creating a bug report using GitHub.

Python version: 3.6.12
Airflow version: 2.0.0a2
Node: 599861bd62ac
-------------------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 2447, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1953, in full_dispatch_request
    return self.finalize_request(rv)
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1970, in finalize_request
    response = self.process_response(response)
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 2269, in process_response
    self.session_interface.save_session(self, ctx.session, response)
  File "/usr/local/lib/python3.6/site-packages/flask/sessions.py", line 387, in save_session
    samesite=samesite,
  File "/usr/local/lib/python3.6/site-packages/werkzeug/wrappers/base_response.py", line 479, in set_cookie
    samesite=samesite,
  File "/usr/local/lib/python3.6/site-packages/werkzeug/http.py", line 1217, in dump_cookie
    raise ValueError("SameSite must be 'Strict', 'Lax', or 'None'.")
ValueError: SameSite must be 'Strict', 'Lax', or 'None'.
```
setup.py
#
#
#
"""Setup.py for the Airflow project."""
import logging
import os
import subprocess
import sys
import unittest
from importlib import util
from os.path import dirname
from textwrap import wrap
from typing import Dict, Iterable, List
from setuptools import Command, find_packages, setup
logger = logging.getLogger(__name__)
spec = util.spec_from_file_location("airflow.version", os.path.join('airflow', 'version.py'))  
mod = util.module_from_spec(spec)
spec.loader.exec_module(mod)  
version = mod.version  
PY3 = sys.version_info[0] == 3
my_dir = dirname(__file__)
try:
    with open(os.path.join(my_dir, 'README.md'), encoding='utf-8') as f:
        long_description = f.read()
except FileNotFoundError:
    long_description = ''
def airflow_test_suite():