Workaround another import problem on update

[mgorny]

Bug: https://bugs.gentoo.org/976616

[mgorny]

Disclaimer: I didn't test it (or reproduced the original issue).

[s7a7ic]

Hi, I had the Bug while updating. So I've applied your commit as a patch to portage and tested it while updating another host and got this error on multiple packages:

Process Process-1224:
Traceback (most recent call last):
  File "/usr/lib/python3.13/multiprocessing/process.py", line 313, in _bootstrap
    self.run()
    ~~~~~~~~^^
  File "/usr/lib/python3.13/multiprocessing/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.13/site-packages/portage/util/_async/ForkProcess.py", line 336, in _bootstrap
  File "/usr/lib/python3.13/site-packages/portage/dbapi/_MergeProcess.py", line 276, in _target
  File "/usr/lib/python3.13/site-packages/portage/dbapi/vartree.py", line 1939, in wrapper
  File "/usr/lib/python3.13/site-packages/portage/dbapi/vartree.py", line 6188, in merge
  File "/usr/lib/python3.13/site-packages/portage/dbapi/vartree.py", line 4368, in treewalk
ModuleNotFoundError: No module named 'portage.util.env_update'

As this was the last host to update, I can't test/reproduce the original issue either.