We should use the `gettempdir` not `tempdir`

[gordonwatts]

func_adl_xAOD/func_adl_xAOD/common/local_dataset.py

Line 86 in 45cafb0

assert tempfile.tempdir is not None

When this access is made, if it is the first in the app to access tempfile, then the tempdir will be none. Use the method gettempdir to see if it is null. Or just remove this assert which is a bit silly anyway.