SCRIPTS: git-show-backports: add "-s" to proposed cherry-pick commands

Since we're using signed-off-by tags for backports, let's add -s to
the command so that we can finally copy-paste it!
diff --git a/scripts/git-show-backports b/scripts/git-show-backports
index ab44eaf..0fad6c1 100755
--- a/scripts/git-show-backports
+++ b/scripts/git-show-backports
@@ -251,10 +251,10 @@
 		echo
 		echo "In order to show and/or apply all leftmost commits to current branch :"
 		echo "   git show ${left_commits[@]}"
-		echo "   git cherry-pick -x ${left_commits[@]}"
+		echo "   git cherry-pick -sx ${left_commits[@]}"
 		echo
 		echo "In order to show and/or apply all rightmost commits to current branch :"
 		echo "   git show ${right_commits[@]}"
-		echo "   git cherry-pick -x ${right_commits[@]}"
+		echo "   git cherry-pick -sx ${right_commits[@]}"
 	fi
 )