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
"""Set final values for options."""
    def run(self):  
        """List extras."""
        print("\n".join(wrap(", ".join(EXTRAS_REQUIREMENTS.keys()), 100)))
def git_version(version_: str) -> str:
    """
    Return a version to identify the state of the underlying git repo. The version will
    indicate whether the head of the current git-backed working directory is tied to a
    release tag or not : it will indicate the former with a 'release:{version}' prefix
    and the latter with a 'dev0' prefix. Following the prefix will be a sha of the current
    branch head. Finally, a "dirty" suffix is appended to indicate that uncommitted
    changes are present.
    :param str version_: Semver version
    :return: Found Airflow version in Git repo
    :rtype: str
    """
    try:
        import git
        try:
            repo = git.Repo(os.path.join(*[my_dir, '.git']))
        except git.NoSuchPathError:
            logger.warning('.git directory not found: Cannot compute the git version')
            return ''
        except git.InvalidGitRepositoryError:
            logger.warning('Invalid .git directory not found: Cannot compute the git version')
            return ''
    except ImportError:
        logger.warning('gitpython not found: Cannot compute the git version.')
        return ''