mcp: update to jsonschema that does not validate structs (#511)

Update to the latest jsonschema commit, which removes the ability to
validate structs and changes the type of ForOptions.TypeSchemas.

examples/server/toolschemas/main_test.go

@@ -0,0 +1,31 @@
+// Copyright 2025 The Go MCP SDK Authors. All rights reserved.
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"testing"
+
+	"github.com/modelcontextprotocol/go-sdk/mcp"
+)
+
+func TestGreet(t *testing.T) {
+	manual, err := newManualGreeter()
+	if err != nil {
+		t.Fatal(err)
+	}
+	res, err := manual.greet(context.Background(), &mcp.CallToolRequest{
+		Params: &mcp.CallToolParamsRaw{
+			Arguments: json.RawMessage(`{"name": "Bob"}`),
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if res.IsError {
+		t.Fatalf("tool error: %q", res.Content[0].(*mcp.TextContent).Text)
+	}
+}