Update dependency django-anymail to v12

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
django-anymail (changelog)	^11.0 -> ^12.0

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Release Notes

anymail/django-anymail (django-anymail)

v12.0

Compare Source

2024-09-09

Breaking changes

* Require **Django 4.0 or later** and Python 3.8 or later.

Features
~~~~~~~~

* **Resend:** Add support for ``send_at``.

Fixes
~~~~~

* **Unisender Go:** Fix several problems in Anymail's Unisender Go status tracking
  webhook. Rework signature checking to fix false validation errors (particularly
  on "clicked" and "opened" events). Properly handle "use single event" webhook
  option. Correctly verify WEBHOOK_SECRET when set. Provide Unisender Go's
  ``delivery_status`` code and unsubscribe form ``comment`` in Anymail's
  ``event.description``. Treat soft bounces as "deferred" rather than "bounced".
  (Thanks to `@MikeVL`_ for fixing the signature validation problem.)

Other
~~~~~

* **Mandrill (docs):** Explain how ``cc`` and ``bcc`` handling depends on
  Mandrill's "preserve recipients" option. (Thanks to `@dgilmanAIDENTIFIED`_
  for reporting the issue.)

* **Postal (docs):** Update links to Postal's new documentation site.
  (Thanks to `@jmduke`_.)

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