Fix import importlib.util

[j-otsuki]

To avoid the following error in Python 3.11.5:

Traceback (most recent call last):
  File "/home/otsuki/venv/python3.11/dcore_e/bin/dcore_pre", line 5, in <module>
    from dcore.dcore_pre import run
  File "/home/otsuki/gitclones/dcore/src/dcore/dcore_pre.py", line 24, in <module>
    from dcore._dispatcher import HDFArchive
  File "/home/otsuki/gitclones/dcore/src/dcore/_dispatcher.py", line 22, in <module>
    if not importlib.util.find_spec(l):
           ^^^^^^^^^^^^^^
AttributeError: module 'importlib' has no attribute 'util'