Consider using `os.path.samefile` for path comparisons in tests

[bpkroth]

trafficstars

        assert os.path.samefile(local_exec_service._temp_dir, path_join(temp_dir, "temp", abs_path=True))

or something like it? + We should probably check for all other places where we compare paths

Originally posted by @motus in https://github.com/microsoft/MLOS/pull/531#discussion_r1352961180

[bpkroth]

FWIW, I don't think this works for files that don't actually exist.