**Apache Airflow version**: 2.0.1

**What happened**:

The operator fails at the last step, after successfully refreshing the workbook with this error:
```
tableauserverclient.server.endpoint.exceptions.ServerResponseError: 

        401002: Unauthorized Access
                Invalid authentication credentials were provided.
```

**What you expected to happen**:
It should not fail, like when we use the username/password authentication method (instead of personal_access_token)

<!-- What do you think went wrong? -->

Tableau server does not allow concurrent connections when using personal_access_token https://github.com/tableau/server-client-python/issues/717
The solution would be redesigning completely the operator to only call the hook once.
My quick fix was to edit this in TableauHook:

```
    def __exit__(self, exc_type: Any, exc_val: Any, exc_tb: Any) -> None:
        pass
```

**How to reproduce it**:

Run this operator TableauRefreshWorkbookOperator using Tableau personal_access_token authentication (token_name, personal_access_token).

airflow/providers/tableau/hooks/tableau.py
if not self.tableau_conn:
            self.tableau_conn = self.get_conn()
        return self
    def __exit__(self, exc_type: Any, exc_val: Any, exc_tb: Any) -> None:
        self.server.auth.sign_out()
    def get_conn(self) -> Auth.contextmgr:
        """
        Signs in to the Tableau Server and automatically signs out if used as ContextManager.
        :return: an authorized Tableau Server Context Manager object.
        :rtype: tableauserverclient.server.Auth.contextmgr
        """
        if self.conn.login and self.conn.password:
            return self._auth_via_password()
        if 'token_name' in self.conn.extra_dejson and 'personal_access_token' in self.conn.extra_dejson:
            return self._auth_via_token()
        raise NotImplementedError('No Authentication method found for given Credentials!')
    def _auth_via_password(self) -> Auth.contextmgr: