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
"apache.hive": hive,
    "apache.kylin": kylin,
    "apache.livy": [],
    "apache.pig": [],
    "apache.pinot": pinot,
    "apache.spark": spark,
    "apache.sqoop": [],
    "celery": celery,
    "cloudant": cloudant,
    "cncf.kubernetes": kubernetes,
    "databricks": databricks,
    "datadog": datadog,
    "dingding": [],
    "discord": [],
    "docker": docker,
    "elasticsearch": [],
    "exasol": exasol,
    "facebook": facebook,
    "ftp": [],
    "google": google,
    "grpc": grpc,
    "hashicorp": hashicorp,
    "http": [],
    "imap": [],
    "jdbc": jdbc,
    "jenkins": jenkins,
    "jira": jira,
    "microsoft.azure": azure,
    "microsoft.mssql": mssql,
    "microsoft.winrm": winrm,