sagemathgh-38515: src/pyproject.toml: Add missing build dep jinja2

    
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- Broken in sagemath#37287
- Reported in
sagemath#37434 (comment)
- Reported in
sagemath#36524 (comment)

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### ⌛ Dependencies

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URL: sagemath#38515
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee