Update .buildkite/hooks/post-checkout

Co-authored-by: Trent Nelson <[email protected]>

.buildkite/hooks/post-checkout

@@ -12,8 +12,7 @@ source ci/env.sh
 (
   echo "+++ Killing stale docker containers"
   while read -r line; do
-    id="$(echo "$line" | awk '{print $1}')"
-    image="$(echo "$line" | awk '{print $2}')"
+    read id image _ <<<"$line"
 
     if [[ $image == *"solanalabs/rust"* ]]; then
       if docker kill "$id" >/dev/null; then