chore: migrate account role test to testcontainers

[escape0707]

Summary

Part of #32454

• Migrates TenantAccountRole.is_privileged_role coverage from the old unit test into the existing Testcontainers account model test.
• Deletes api/tests/unit_tests/models/test_account.py.
• Removes models/test_account.py from the Testcontainers Ruff and Pyrefly exclusion lists after cleaning the touched target file.

Targeted verification:

• uv run ruff check tests/test_containers_integration_tests/models/test_account.py
• uv run pyrefly check tests/test_containers_integration_tests/models/test_account.py --summary=none --output-format=min-text
• DOCKER_HOST=unix:///run/user/1000/podman/podman.sock uv run pytest tests/test_containers_integration_tests/models/test_account.py

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods

[github-actions]

Pyrefly Type Coverage

Metric	Base	PR	Delta
Type coverage	51.34%	51.34%	+0.00%
Strict coverage	50.85%	50.86%	+0.00%
Typed symbols	30,576	30,576	0
Untyped symbols	29,255	29,254	-1
Modules	2930	2929	-1