Add infrastructure for validating stand-alone Python files in samples

[swernli]

Right now, new Q# projects added to samples get automatically picked up and compiled in CI, along with stand-alone Q# in certain folders. CI also runs most notebooks to confirm cells execute without error. But for samples like those added #1858 that include a stand-alone Python file nothing in CI runs the code to confirm we aren't breaking the Python scripts. We should have something that runs these files in CI so we don't accidentally introduce breaking changes for them.