Update python version in pyproject toml

## Checklist before submitting an issue

- [x] I have checked the [existing issues](https://github.com/NLeSC/python-template/issues) and couldn't find an issue about this bug.

## Issue details
This should be 3.10:
https://github.com/NLeSC/python-template/blob/eb1f02cf8945b6bdf02953681762d6683118f1ae/template/pyproject.toml.jinja#L40