resolve OpenMDAO deprecating self.set_design_var in Drivers for self._set_design_var

[jaredthomas68]

…_set_design_var

Purpose

Resolve OpenMDAO deprecating self.set_design_var in Drivers for self._set_design_var. This change makes WISDEM compatible with OpenMDAO 3.45. This fix is needed for tests to pass for H2Integrate, so getting these into the release version very soon would be helpful.

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

Run tests, specifically wisdem/test/test_optimization_drivers/test_nsga2_driver.py

Checklist

• I have run existing tests which pass locally with my changes
• [-] I have added new tests or examples that prove my fix is effective or that my feature works
• [-] I have added necessary documentation

[jaredthomas68]

Closing as duplicate of #734