Update copyright year (#83)

Workflow: update copyright year, run: 4

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

README.rst

@@ -70,7 +70,7 @@ For code linting::
 Copyright and Terms of Use
 --------------------------
 
-Copyright (C) 2008-2023 NIWA & British Crown (Met Office) & Contributors.
+Copyright (C) 2008-2024 NIWA & British Crown (Met Office) & Contributors.
 
 Cylc is free software: you can redistribute it and/or modify it under the terms
 of the GNU General Public License as published by the Free Software Foundation,