Update pyproject.toml

[aminalaee]

Summary

Remove mypy no_implicit_optional=True as it is True by default.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.

[Kludex]

Thanks Amin 🙏

Let's hang out this week, if you are in Utrecht. 👍