fix: JSONRPCResponse JavaDoc

[vorburger]

Fix the clearly wrong JavaDoc on the McpSchema.JSONRPCResponse.

Motivation and Context

Triggered by reading it while debugging #605.

Complimentary to #607.

How Has This Been Tested?

N/A, as it's just a JavaDoc fix.

Breaking Changes

No, as it's just a JavaDoc fix.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

[vorburger]

@tzolov just like for #607, do you want to approve the 1st contrib workflow to run, and review and merge if OK?