Necessary updates for using pixi

[LisaBock]

For the recent release, pixi is used for installing ESMValTool. Therefore, the tutorial episode "Development and Contribution" is updated.

Tasks

• Give this pull request a descriptive title.
• If you are contributing to existing lesson materials, please make sure the content conforms to the Lesson development section in CONTRIBUTING.md and does not contain any spelling or grammatical errors.
• If you are making a new episode, please make sure the content conforms to the Lesson organization and Lesson formatting sections in CONTRIBUTING.md and does not contain any spelling or grammatical errors.
• Preferably Codacy checks pass. Status can be seen below your pull request. If there is an error, click the link to find out why.
• Preview changes on your machine before pushing them to GitHub by running make serve, alternatively make docker-serve. Please see the Previewing your changes locally section in CONTRIBUTING.md for installation instructions.
• All code instructions have been tested.

If you need help with any of the tasks above, please do not hesitate to ask by commenting in the issue or pull request.

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Closes #434

[hb326]

Hey @LisaBock,
thanks for updating the episode! I added some suggested rephrasing to the text, but otherwise I think this is great. Thanks!

[LisaBock]

Thanks @hb326 ! I followed your suggestions. Should be fine now...

[hb326]

Thanks, @LisaBock, for the changes! I found two more small things...

[LisaBock]

@hb326 Thanks! Done!

[hb326]

Great! Thanks @LisaBock!