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
]
snowflake = [
    'snowflake-connector-python>=1.5.2',
    'snowflake-sqlalchemy>=1.1.0',
]
spark = [
    'pyspark',
]
ssh = [
    'paramiko>=2.6.0',
    'pysftp>=0.2.9',
    'sshtunnel>=0.1.4,<0.2',
]
statsd = [
    'statsd>=3.3.0, <4.0',
]
tableau = [
    'tableauserverclient~=0.12',
]
vertica = [
    'vertica-python>=0.5.1',
]
virtualenv = [
    'virtualenv',
]
webhdfs = [
    'hdfs[avro,dataframe,kerberos]>=2.0.4',
]
winrm = [
    'pywinrm~=0.4',