Fix plot_wingbox.py to work for matplotlib v3.8+

[shamsheersc19]

Purpose

Fix plot_wingbox.py to work for matplotlib v3.8+.
The dist attribute for 3-D plots has been deprecated in recent matplotlib versions.
See Issue #423

Expected time until merged

1 day
Code review should only take a few minutes.

Type of change

Bugfix (non-breaking change which fixes an issue)

Testing

Run the wingbox example in the examples dir (can reduce "num_y" to 15 and "num_x" to 3 to decrease run time) and call the plot_wingbox script (usage: python ../utils/plot_wingbox.py aerostruct.db).
Tested with matplotlib versions:

• 3.6.0
• 3.7.0
• 3.8.0
• 3.8.3

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
• [ x] 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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.56%. Comparing base (def4df0) to head (4f225cf).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #424      +/-   ##
==========================================
- Coverage   94.51%   92.56%   -1.95%     
==========================================
  Files         104      104              
  Lines        6470     6470              
==========================================
- Hits         6115     5989     -126     
- Misses        355      481     +126     

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[kanekosh]

Thank you Sham!

[eytanadler]

@shamsheersc19 if you are willing, could you also make this fix in the plot_wing.py file? I think it has the same problem.

[shamsheersc19]

@shamsheersc19 if you are willing, could you also make this fix in the plot_wing.py file? I think it has the same problem.

@eytanadler thanks for pointed that out. I just created a new PR for it.

Thanks for the quick turnaround @kanekosh and @eytanadler.