`python-sdk-tutorial.ipynb` shows outdated comments

[giuliosmall]

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When initialising Looker SKD with Python, the example on Google Collab shows:

Now that we've set all the necessary environment variables, we should be able to initialize the Looker SDK. When initializing the SDK, you choose which version to use— 3.1 or 4.0. The 4.0 SDK has some new endpoints and bug fixes, but is still experimental.

While the official documentation:

Note: As of Looker 22.4, the [Looker API 4.0 is generally available](https://cloud.google.com/looker/docs/api-4-ga). In Looker 23.18, the [Looker API 3.1 has been removed](https://cloud.google.com/looker/docs/api-3x-deprecation).