Merge pull request #16689 from tamiko/update_copyright_script

contrib/utilities/update-copyright.sh: several improvements

diff --cc contrib/utilities/update-copyright.sh
index f5cfd372718e5c84d84ecfed6594a5f2ec499edd,f96f4a3c610376286cfa4b0c1c33b94f92ddc9e6..4ce09495477fe0b670ae3c6d4e3e697449a094a1
--- 1/contrib/utilities/update-copyright.sh
--- 2/contrib/utilities/update-copyright.sh
+++ b/contrib/utilities/update-copyright.sh
@@@ -6,13 -5,16 +6,14 @@@
  ##
  ## This file is part of the deal.II library.
  ##
 -## The deal.II library is free software; you can use it, redistribute
 -## it, and/or modify it under the terms of the GNU Lesser General
 -## Public License as published by the Free Software Foundation; either
 -## version 2.1 of the License, or (at your option) any later version.
 -## The full text of the license can be found in the file LICENSE.md at
 -## the top level directory of deal.II.
 +## Part of the source code is dual licensed under Apache-2.0 WITH
 +## LLVM-exception OR LGPL-2.1-or-later. Detailed license information
 +## governing the source code and code contributions can be found in
 +## LICENSE.md and CONTRIBUTING.md at the top level directory of deal.II.
  ##
 -## ---------------------------------------------------------------------
 +## ------------------------------------------------------------------------
  
+ set -u
  
  # Purpose: Update the copyright year of every file based on the last
  #          modification recorded in the git logs