Bump django-anymail from 6.0.1 to 7.0.0

Bumps [django-anymail](https://github.com/anymail/django-anymail) from 6.0.1 to 7.0.0.
- [Release notes](https://github.com/anymail/django-anymail/releases)
- [Changelog](https://github.com/anymail/django-anymail/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/anymail/django-anymail/compare/v6.0.1...v7.0

)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>