load_texture: fix usage of importlib

[rbignon]

To use importlib.util, you need to import it.

>>> import importlib
>>> importlib.util.find_spec
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'importlib' has no attribute 'util'
>>> import importlib.util
>>> importlib.util.find_spec
<function find_spec at 0x7f817485c400>

[pokepetter]

Can't reproduce. Which Python version are you using?

[rbignon]

Python 3.12.4