Mailjet deleted the Anymail testing account without notice.
Recreating the account changed the test template id. Move
the id to an environment variable to simplify changing it.
For CI/CD tasks not testing a specific Python version, switch to Python 3.12.
(Had been using mixture of 3.10 and 3.11. GitHub's ubuntu-22.04 runner has
Python 3.10 installed by default, but 3.12 should be in the tool cache.)
- Replace "SendinBlue" with "Brevo"
throughout the code.
- Maintain deprecated compatibility
versions on the old names/URLs.
(Split into separate commit
to make renamed files more
obvious.)
- Update docs to reflect change,
provide migration advice.
- Update integration workflow.
* Split test, integration-test, and release workflows,
simplifying config and logic for each.
* Use environment to separate secrets for release workflow.
* Update test matrix with newer Django and Python versions.