Update to latest gnulib with new copyright year.
Run "make update-copyright" and then...
* gnulib: Update included in this commit as copyright years
are the only change from the previous gnulib commit.
* tests/init.sh: Sync with gnulib to pick up copyright year.
* bootstrap: Likewise.
* tests/sample-test: Adjust to use the single most recent year.
* src/printf.c (print_formatted): Add support for %i$ indexed args.
* tests/printf/printf-indexed.sh: Add a new file of test cases.
* tests/local.mk: Reference the new test file.
* doc/coreutils.texi (printf invocation): Mention how mixed
processing of indexed and sequential references are supported,
unlike the printf(2) library function.
* NEWS: Mention the new (POSIX:2024) feature.
Addresses https://bugs.gnu.org/73068