Meta: Extend Celery/Redis integration tests (Tier 1 + Tier 2)

[berendt]

Context

#2368 laid the foundation for integration tests: the python-osism-integration-tests Zuul job (playbooks/test-integration.yml) starts a single redis:7-alpine container, installs the package with pipenv, and runs pytest tests/integration with REDIS_HOST=localhost and OSISM_REQUIRE_REDIS=1. The shared infrastructure — skip-when-Redis-unreachable logic plus the celery_app / celery_worker session fixtures — lives in tests/integration/conftest.py.

Three test modules exist so far:

• test_celery.py — noop round-trip + worker visibility
• test_locking.py — Redlock + task-lock round-trip
• test_redis_streams.py — task-output push/finish/fetch

This meta issue tracks the next round of integration tests. The guiding principle: first exhaust everything that works with the existing single-Redis infrastructure (Tier 1), then add the few tests that need only one extra test dependency (Tier 2 — httpx for the FastAPI TestClient). Tests that require additional services (RabbitMQ, NetBox, OpenStack) are explicitly out of scope here and will be tracked separately.

All new tests live under tests/integration/, carry pytestmark = pytest.mark.integration, stay green locally (skipped without Redis), and run for real in CI.

Tier 1 — no infrastructure change (Redis only)

• Integration test: RedisSemaphore / create_netbox_semaphore #2401 — RedisSemaphore / create_netbox_semaphore
• Integration test: Ansible vault password round-trip #2402 — Ansible vault password round-trip
• Integration test: check_ansible_facts freshness #2403 — check_ansible_facts freshness
• Integration test: Celery error, state and revoke paths #2404 — Celery error / state / revoke paths
• Integration test: EventBridge Redis pub/sub round-trip #2405 — EventBridge Redis pub/sub round-trip

Tier 2 — one extra test dependency (httpx for FastAPI TestClient)

Shared prerequisite: add httpx to [dev-packages] in Pipfile so fastapi.testclient.TestClient is importable. fastapi itself is already a runtime dependency.

• Integration test: API facts endpoints (FastAPI TestClient + Redis) #2406 — API facts endpoints via FastAPI TestClient
• Integration test: WebSocket /v1/events/openstack (FastAPI TestClient) #2407 — WebSocket endpoint /v1/events/openstack via TestClient