Fix propagation of the remote-execution-append-only-caches path  (#17469)
Fix propagation of the remote-execution-append-only-caches path  (#17469)

PyO3 will (generally helpfully) default all trailing `Option` arguments of a function to `None`.

It would definitely be worth the time to port [ExecutionOptions](https://github.com/pantsbuild/pants/blob/7ffcc21c916b7d884513d36cd2bb3cb1f5989c10/src/python/pants/option/global_options.py#L472-L473) to a PyO3 type to skip this manual conversion, but best for a followup.
pantsbuild/pants,pantsbuild/pants,pantsbuild/pants,pantsbuild/pants,pantsbuild/pants,pantsbuild/pants,pantsbuild/pants