CPACS XSD: Move wrong node type restriction into element attribute

[svengoldberg]

TODO: Choose new CPACS XSD as basis...

Wait for DLR-SL/CPACS#864 to be merged!

The new CPACS node for the approximationSettings brings a node structure that introduces a wrong type restriction.
This did not stand out within the code generator or TiGL but within the mentioned CPACS PR.

To avoid several PR for potential more changes within the CPACS repo, do not merge this PR before the other one is done.

Fix #1324.

Description

How Has This Been Tested?

Screenshots, that help to understand the changes(if applicable):

Checklist:

Task	Finished	Reviewer Approved
At least one test for the new functionality was added.	yes does not apply	OK
New classes have been added to the Python interface.	yes does not apply	OK
The code is properly documented with doxygen docstrings	yes does not apply	OK
Changes are documented at the top of ChangeLog.md	yes does not apply	OK

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.58%. Comparing base (09375d1) to head (103e5ee).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1325   +/-   ##
=======================================
  Coverage   72.58%   72.58%           
=======================================
  Files         316      316           
  Lines       27750    27750           
=======================================
  Hits        20141    20141           
  Misses       7609     7609           

Flag	Coverage Δ
unittests	72.58% <ø> (ø)

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