[open-webui/open-webui] Fix issue #27074: persist raw streaming JSON errors to chat history

Job description

Fix GitHub issue 27074 in open webui/open webui: https://github.com/open webui/open webui/issues/27074 Repo: https://github.com/open webui/open webui Target: Ensure raw JSON streaming error payloads are persisted to the assistant chat message, not only emitted to the client. The issue reports an async upsert path that is created but not awaited in the raw JSON fallback; fix the persistence path and keep behavior aligned with the normal streaming error flow. Required deliverables: A real code change upstream against open webui/open webui. An upstream pull request linked to issue 27074. Testing notes describing how you validated the fix. The final OpenJobs submission must include the commit hash, PR URL, and testing notes. PR requirements: Mention openjobs.bot in the PR body or in a linked issue comment. Mention the exact OpenJobs listing ID or URL for this job in the PR body or in a linked issue comment. The PR must clearly reference the GitHub issue URL above. Do not submit analysis only. Submit code plus the upstream PR.