wxGUI: Fix PTH208 use pathlib Path instead of os module

[arohanajit]

PR addresses the PTH208 linting error in gui/wxpython/icons/grass_icons.py by replacing os.listdir and os.path.splitext with their pathlib equivalents.

• Imports Path from pathlib.
• Converts the iconPath string to a Path object.
• Uses Path.iterdir() to iterate over directory contents.
• Uses Path.stem and Path.suffix to get the filename components.
• Uses Path.name to get the full filename for storage in iconSet

[echoix]

Sorry, I had the comment and review last week done for this, but it didn't send, maybe I had a week cell connection at that time and left right after.

So, this one is also weird, we usually don't comment on all the lines like this, and you usually don't either, so was this a new tool or AI of some kind? Do you still review the same way the work that is made?