Odoo 19: Restore FastAPI retrying HttpCase tests

[jeremi]

Background

FastAPI retrying tests are skipped on Odoo 19 because they currently return HTTP 500 in test mode.

Skipped tests

• test_retrying
• test_retrying_post

Goal

Identify root cause and restore assertions that verify retry behavior for GET and POST flows.

Acceptance criteria

• Remove skip decorators from both tests.
• Tests pass under Odoo 19 CI.
• Retry behavior is validated end-to-end.

References

• fastapi/tests/test_fastapi.py