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
version=version,
        packages=find_packages(
            include=['airflow*'],
            exclude=exclude_patterns),
        package_data={
            'airflow': ['py.typed'],
            '': ['airflow/alembic.ini', "airflow/git_version", "*.ipynb",
                 "airflow/providers/cncf/kubernetes/example_dags/*.yaml"],
            'airflow.api_connexion.openapi': ['*.yaml'],
            'airflow.serialization': ["*.json"],
        },
        include_package_data=True,
        zip_safe=False,
        entry_points={
            "console_scripts": [
                "airflow = airflow.__main__:main",
            ],
        },
        install_requires=INSTALL_REQUIREMENTS,
        setup_requires=[
            'bowler',
            'docutils',
            'gitpython',
            'setuptools',
            'wheel',
        ],
        extras_require=EXTRAS_REQUIREMENTS,
        classifiers=[
            'Development Status :: 5 - Production/Stable',
            'Environment :: Console',