Update the planification

[RondeauG]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes #xyz
• (If applicable) Documentation has been added / updated (for bug fixes / features).
• (If applicable) Tests have been added.
• CHANGES.rst has been updated (with summary of main changes).
  • Link to issue (:issue:number) and pull request (:pull:number) has been added.

What kind of change does this PR introduce?

• Updates the planification figure.

Does this PR introduce a breaking change?

Other information:

[Zeitsperre]

We might want to mention the remaining work needed for building out the testing data registry now that we have a pooch-based data fetching mechanism and xhydro-testdata configured.