chore: update copyright year to 2026 (#537)

Author: zhjwpku

LICENSE

@@ -222,7 +222,7 @@ This product includes code from Apache Arrow.
   * cmake_modules/IcebergBuildUtils.cmake.
   * cmake_modules/IcebergThirdpartyToolchain.cmake.
 
-Copyright: 2016-2025 The Apache Software Foundation.
+Copyright: 2016-2026 The Apache Software Foundation.
 Home page: https://arrow.apache.org/
 License: https://www.apache.org/licenses/LICENSE-2.0
 

NOTICE

@@ -1,5 +1,5 @@
 Apache Iceberg C++
-Copyright 2024-2025 The Apache Software Foundation
+Copyright 2024-2026 The Apache Software Foundation
 
 This product includes software developed at
 The Apache Software Foundation (http://www.apache.org/).