Update django-localflavor and pin to specific versions in pyproject.toml

This MR contains the following updates:

Package	Type	Update	Change
django-localflavor	dev-dependencies	major	~2.1 -> latest git revision

I do not want to wait for a release, the code does seem stable as is. And this is required for django 3.0.

This MR also pins the versions in pyproject.yml so that renovate can update all, since apparently it's missing stuff.