Test ghost for forests with holes

[lukasdreyer]

Describe your changes here:
Ghost currently does not work on forests with deleted elements. This test is an example of a configuration that fails.
See #825.
It does not fail when the second adapt call is done without ghosts

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Licence

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[lukasdreyer]

In the spellcheck and indent commit, I accidentally committed the version, that does not compute ghosts and therefore does not throw an error

[holke]

Please refer to the new guidelines for test driven development: https://github.com/DLR-AMR/t8code/wiki/Test-driven-development

[Davknapp]

Looks good to me, if @holke is fine with it, we can merge it.

[holke]

Approved.
@lukasdreyer is there a reason why its still in draft mode or can we take it out of draft and merge?

[lukasdreyer]

Approved. @lukasdreyer is there a reason why its still in draft mode or can we take it out of draft and merge?

No reason, I just forgot about it.