Fix exception thrown on Python 3.8 for checkpackage.py
According to official documentation, I don't see how it used to work before
The generated exception is:
Traceback (most recent call last):
File "checkpackages.py", line 50, in <module>
installed = {pkg.name for pkg in importlib.metadata.distributions()}
File "checkpackages.py", line 50, in <setcomp>
installed = {pkg.name for pkg in importlib.metadata.distributions()}
AttributeError: 'PathDistribution' object has no attribute 'name'
This would prevent import/export in opentimelineio and would also prevent checking the python environment (at least on Windows)
The irony is that I was looking for a totally different feature but was sure that fixing this would help. Anyway, I hope it can be useful.