Add babel to dev requirement

[user202729]

Summary of changes

As in the title. I think this is reasonable enough, you need babel to build the package (but mostly if I want to pip install -e . --verbose --no-build-isolation, even though the official development guide recommend tox)

note that it's already included in setup.txt, so an alternative is to add -r setup.txt. I don't know what wheel package is for though.

Pull Request Checklist

• Changes have tests
• News fragment added in news.d. See documentation for details (no new feature, should be unimportant)

[mkrnr]

Thanks!