Bring compose file for CI tests into parity with main env

[mihow]

Summary

• Ensure tests only use the one processing service available in tests (ignore what might be in local .env)
• Update minio settings and try to fix spurious 403 Forbidden errors for minio (is it that minio_init isn't always completing successfully? that is what sets public permissions on the buckets)

[netlify]

✅ Deploy Preview for antenna-preview canceled.

Name	Link
🔨 Latest commit	298f6ff
🔍 Latest deploy log	https://app.netlify.com/projects/antenna-preview/deploys/689e95ab6d337f00088e38ca

[Copilot]

Pull Request Overview

This PR brings the CI testing environment configuration into alignment with the main environment setup by updating Docker Compose settings and adding environment variables to ensure consistent test execution.

• Updates PostgreSQL service to use a custom Dockerfile instead of the standard image
• Enhances MinIO configuration with health checks and security settings to address intermittent 403 errors
• Configures a default processing service for CI tests to ensure consistent behavior

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
docker-compose.ci.yml	Updates PostgreSQL to use custom build and adds MinIO health checks and security configuration
.envs/.ci/.django	Adds default processing service configuration for CI environment

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}