Fix copyright year in disable_warnings.h

Change-Id: I99359e53e75732ff515897ac4a01c13793748b3c

include/ceres/internal/disable_warnings.h

diff --git a/include/ceres/internal/disable_warnings.h b/include/ceres/internal/disable_warnings.h
index 02807cd..c7c1dbc 100644
--- a/include/ceres/internal/disable_warnings.h
+++ b/include/ceres/internal/disable_warnings.h
@@ -1,5 +1,5 @@
 // Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2025 Google Inc. All rights reserved.
+// Copyright 2026 Google Inc. All rights reserved.
 // http://ceres-solver.org/
 //
 // Redistribution and use in source and binary forms, with or without