Run "TZ=UTC0 admin/update-copyright".
* admin/diff-tar-files: * admin/merge-gnulib: * admin/merge-pkg-config: * admin/update-copyright: * build-aux/git-hooks/prepare-commit-msg: * make-dist: Fix some shellcheck linter warnings.
Run "TZ=UTC0 admin/update-copyright $(git ls-files)".
* build-aux/git-hooks/prepare-commit-msg: If someone occasionally puts Signed-off line, it will likely get there through -s option of git. Exploit this fact to abort before a user got a chance to type commit message. (Bug#35368)