setup: avoid the deprecated `distutils.spawn.find_executable` I noticed this was flagged with `DeprecationWarning` in py3.12 with `setuptools` 74.1.2, and it suggested `shutil.which()` instead. The signatures aren't the same, but the additional `mode` argument in the middle of the latter defaults to `os.F_OK | os.X_OK`, which maintains the same semantics.