Add a GitHub Actions test workflow

[swryan]

For your consideration, I put together a basic test workflow based on the OpenMDAO workflow that would run automatically on pull requests and merges to the master branch.

There are three failing tests, all out of bounds errors on compressor and turbine maps (see below).

If there is a fix for these or if you want to just skip those tests, I can do that, otherwise you are welcome to take this and do what you want with it (including nothing).

The following tests failed:
test_compressor.py:CompressorTestCase.test_case1
test_compressor_od.py:CompressorODTestCase.test_case1
test_turbine.py:TurbineTestCase.test_case1

openmdao.core.analysis_error.AnalysisError: 'compressor.map.map' <class MetaModelStructuredComp>: Error interpolating output 'WcMap' because input 'compressor.map.map.alphaMap' was out of bounds ('0.0', '90.0') with value '-1e-06'

openmdao.core.analysis_error.AnalysisError: 'turbine.map.readMap' <class MetaModelStructuredComp>: Error interpolating output 'WpMap' because input 'turbine.map.readMap.alphaMap' was out of bounds ('1.0', '2.0') with value '0.999999'