Fixed paths to code in docs

[eytanadler]

Purpose

The test file locations were moved in a previous PR, which broke code blocks in the docs. This PR fixes the paths so they appear again.

Expected time until merged

Type of change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update
• Maintenance update
• Other (please describe)

Testing

Checklist

• I have run flake8 and black to make sure the Python code adheres to PEP-8 and is consistently formatted
• I have formatted the Fortran code with fprettify or C/C++ code with clang-format as applicable
• I have run unit and regression tests which pass locally with my changes
• I have added new tests that prove my fix is effective or that my feature works
• I have added necessary documentation

[kanekosh]

Thanks Eytan. I should've caught this when I reviewed, my bad.

Could you also update the paths in other files:

• quick_example.rst
• struct_example.rst
• aerostruct_tube_walkthrough.rst
• advanced_features/aerostruct_ffd.rst
• advanced_features/ground_effect.rst
• advanced_features/multiple_surfaces.rst
• advanced_features/multipoint.rst

I think this is all but I might've missed something

[eytanadler]

Is this good to merge?