copy: reduce verbosity of -i and -u with --verbose

copy: reduce verbosity of -i and -u with --verbose

Since skipping of files is central to the operation of -i and -u,
and with -u one may be updating few files out of many,
reinstate the verbosity of this functionality as it was before 9.3.

* src/copy.c (copy_internal): Only output "skipped" message
with --debug.  Also adjust so message never changes with --debug.
* tests/cp/cp-i.sh: Adjust accordingly.
* tests/mv/mv-n.sh: Likewise.
* tests/cp/debug.sh: Add explicit test case for message.
* NEWS: Mention the change in behavior.