fix: fix cannot extract elements from a scalar

[fatelei]

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Summary

fix #36768

Screenshots

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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	45.79%	45.79%	+0.00%
Strict coverage	45.31%	45.31%	+0.00%
Typed symbols	24,556	24,557	+1
Untyped symbols	29,380	29,381	+1
Modules	2741	2741	0