xfs_scrub_media_fail: reduce security lockdowns to avoid postfix problems

xfs_scrub_media_fail: reduce security lockdowns to avoid postfix problems

The same lockdown logic of commit 9042fcc08eed6a ("xfs_scrub_fail:
tighten up the security on the background systemd service") was applied
to the media scan failure reporting service.  Therefore, it's also
broken on systems that have setgid mailer programs (e.g. postfix).
Fix this by applying the same change from commit 15fd6fc686d5ce here
too.

Cc: linux-xfs@vger.kernel.org # v6.17.0
Fixes: 15fd6fc686d5ce ("xfs_scrub_fail: reduce security lockdowns to avoid postfix problems")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Fixes: 45ec29cfba02 ("xfs_scrub_all: support metadata+media scans of all filesystems")
Reviewed-by: Andrey Albershteyn <aalbersh@kernel.org>