update schema url point to the actual location (#884)

<!-- Provide a brief summary of your changes -->

## Motivation and Context
This PR ensures that the draft URL points to the actual draft schema 
improvement suggested in
https://github.com/modelcontextprotocol/registry/issues/814


## How Has This Been Tested?
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tested? -->

## Breaking Changes
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## Types of changes
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the boxes that apply: -->
- [x] 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
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that apply. -->
- [ ] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [ ] 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

## Additional context
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tools/validate-examples/main.go

@@ -57,7 +57,7 @@ func runValidation() error {
 		},
 	}
 
-	schemaPath := filepath.Join("docs", "reference", "server-json", "server.schema.json")
+	schemaPath := filepath.Join("docs", "reference", "server-json", "draft", "server.schema.json")
 	baseSchema, err := compileSchema(schemaPath)
 	if err != nil {
 		return fmt.Errorf("failed to compile server.schema.json: %w", err)