Bump django-anymail[mailgun] from 11.0.1 to 13.0

Bumps [django-anymail[mailgun]](https://github.com/anymail/django-anymail) from 11.0.1 to 13.0.
- [Release notes](https://github.com/anymail/django-anymail/releases)
- [Changelog](https://github.com/anymail/django-anymail/blob/main/CHANGELOG.rst)
- [Commits](anymail/django-anymail@v11.0.1...v13.0)

---
updated-dependencies:
- dependency-name: django-anymail[mailgun]
  dependency-version: '13.0'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

requirements/production.txt

@@ -7,4 +7,4 @@ psycopg[c]==3.2.1  # https://github.com/psycopg/psycopg
 
 # Django
 # ------------------------------------------------------------------------------
-django-anymail[mailgun]==11.0.1  # https://github.com/anymail/django-anymail
+django-anymail[mailgun]==13.0  # https://github.com/anymail/django-anymail