test(api): make session decorator path assertion platform-agnostic

[AlexMultiAgent]

test(api): make session decorator path assertion platform-agnostic

Fixes #39890

Summary

• Normalize co_filename before comparing it in test_post_uses_one_session_and_rolls_back_when_signal_fails so the decorator unwrap loop terminates on Windows as well as POSIX.
• No production behavior changes.

Root cause

The test walks the decorator chain with co_filename.endswith("controllers/common/session.py"). On Windows co_filename contains backslashes, so the condition never matches and the loop unwraps past the end of the chain, raising AttributeError: 'function' object has no attribute '__wrapped__'. The chain itself is intact.

Validation

• Windows (Python 3.12): the previously failing test now passes.
• Backend: test_model_config_api.py passes on POSIX as well.

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

From Codex