toolbox: Fix argument injection

BUG=b/507605835
TEST=presubmit
RELEASE_NOTE=None

Change-Id: I1230409aa14779b3934207aee4af488231e27cfb

toolbox

diff --git a/toolbox b/toolbox
index 61c4061..5c6a889 100755
--- a/toolbox
+++ b/toolbox
@@ -58,7 +58,7 @@
 if [ ! -f ${osrelease} ] ; then
 	sudo mkdir -p "${machinepath}"
 	sudo mkdir -p "${TOOLBOX_TEMP_DIR}"
-	sudo chown ${USER}: "${machinepath}"
+	sudo chown "${USER}": "${machinepath}"
 
 	if [ ! -z "${TOOLBOX_DOCKER_IMAGE_TARBALL}" ] ; then
 		sudo ctr image import "${TOOLBOX_DOCKER_IMAGE_TARBALL}"