Fix 11979

[wangiii]

Fix this issue
…s during execution if there are variables in the prompt text.

Fix #11979

Summary

Fix the bug in the workflow's llm node, if the system prompts that there are variables in the text, the execution will report an error.

Tip

Close issue syntax: Fixes #<issue number> or Resolves #<issue number>, see documentation for more details.

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Checklist

Important

Please review the checklist below before submitting your pull request.

• 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 dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[crazywoola]

Please fix the errors in CI.

[wangiii]

Please fix the errors in CI.

Already fixed.