fix typo in code example on MCP tools

[song-flying]

Description

Fix typo in the code sample under MCP tools on Tools Overview page

Type of Change

• New content addition
• Content update/revision
• Structure/organization improvement
• Typo/formatting fix
• Bug fix
• Other (please describe):

Typo/formatting fix

Motivation and Context

Areas Affected

Tools Overview --> Building & Loading Tools --> 2. Model Context Protocol (MCP) Tools

Screenshots

Checklist

• I have read the CONTRIBUTING document
• My changes follow the project's documentation style
• I have tested the documentation locally using mkdocs serve
• Links in the documentation are valid and working
• Images/diagrams are properly sized and formatted
• All new and existing tests pass

Additional Notes

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