running make shellcheck required shellcheck to be
installed locally in the $PATH.
This change renders make shellcheck self-contained
by installing shellcheck in the local tools cache directory
likeit is already done with other tools.
Signed-off-by: Michael Adam <obnox@samba.org>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>