Bump django-anymail[mailgun] from 11.1 to 12.0

Bumps [django-anymail[mailgun]](https://github.com/anymail/django-anymail) from 11.1 to 12.0.
- [Release notes](https://github.com/anymail/django-anymail/releases)
- [Changelog](https://github.com/anymail/django-anymail/blob/main/CHANGELOG.rst)
- [Commits](anymail/django-anymail@v11.1...v12.0)

---
updated-dependencies:
- dependency-name: django-anymail[mailgun]
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

config/requirements/production.txt

@@ -7,4 +7,4 @@ psycopg==3.2.1 # https://github.com/psycopg/psycopg
 
 # Django
 # ------------------------------------------------------------------------------
-django-anymail[mailgun]==11.1  # https://github.com/anymail/django-anymail
+django-anymail[mailgun]==12.0  # https://github.com/anymail/django-anymail