Python 3.9 make issue

[developersteve]

This is a heads up for anyone that has python 3.9 locally if you get the error (i got it on OSX)

Error: PythonPipBuilder:Resolver - Path resolution for runtime: python3.8 of binary: python was not successful

product-mock.yaml and shoppingcart-service.yaml will break the make backend unless you update the runtime to python 3.9 in those files