MissingIDFieldWarning in Tutorial 18

[bilgeyucel]

Describe the issue
When generate_markdowns.py script is run, Tutorial 18 gives this warning:

/opt/homebrew/Caskroom/miniforge/base/lib/python3.10/site-packages/nbformat/__init__.py:92: MissingIDFieldWarning: Code cell is missing an id field, this will become a hard error in future nbformat versions. You may want to use `normalize()` on your notebooks before validations (available since nbformat 5.1.4). Previous versions of nbformat are fixing this issue transparently, and will stop doing so in the future.
  validate(nb)

I encountered this only with Tutorial 18.

To Reproduce
Run python scripts/generate_markdowns.py --index index.toml --notebooks tutorials/18_GPL.ipynb --output markdowns/

Expected behavior
Although I couldn't figure out why this happens, this warning might be something important. We should check it.

What environment did you try to run the tutorial on?:

• OS: macOS, VSCode terminal
• pip install --upgrade pip and pip install -r requirements.txt are run