Update WindowMPS example

[VicVanderLinden]

Updating the example of windowMPS so it can run in latest version

[github-actions]

Your PR no longer requires formatting changes. Thank you for your contribution!

[lkdvos]

Thanks for helping out, I greatly appreciate this!
It seems like there are still some small formatting changes required, would you mind also changing that?

In the future, it would be nice to promote this to a full example that we can actually include in the documentation. If this is something you are interested in, I'm definitely happy to help you get that set up.

[VicVanderLinden]

Hi, thanks! I am still getting the hang of Github but I definitely would be open to doing something like that. Maybe an entire example showing the WindowMPS for an improved version of https://arxiv.org/abs/1907.02474 would be nice?

[codecov]

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[lkdvos]

That would definitely be great! If you have the time to start putting together a script, in whatever form you like, it is then straightforward to incorporate it in the docs. I will already merge this once the tests pass, as I think it is already a great improvement, but I would definitely love to improve on that.