fix: use _cleanup hook instead of overriding cleanup()

download-artifacts.sh sources library.sh which already registers
`trap cleanup EXIT`. Defining a local cleanup() was overriding the
library's version and breaking the standard cleanup chain (killing
child processes). Rename to _cleanup() so it participates in the
hook mechanism correctly, and drop the redundant trap registration.

Author: abtreece

internal-scripts/ci-cd/download-artifacts.sh

@@ -16,7 +16,7 @@ CI_ARTIFACTS_RUN_NUMBER=${CI_ARTIFACTS_RUN_NUMBER:-$GITHUB_RUN_NUMBER}
 CLEAR=${CLEAR:-false}
 TMPDIR=${TMPDIR:-/tmp}
 
-function cleanup()
+function _cleanup()
 {
     if [[ -n "$WORK_DIR" ]]; then
         rm -rf "$WORK_DIR"
@@ -39,7 +39,6 @@ echo
 
 echo "--> Downloading artifacts"
 WORK_DIR=$(mktemp -d "$TMPDIR/XXXXXX")
-trap cleanup EXIT
 mkdir -p "$ARTIFACT_PATH"
 gsutil -m cp "${URLS[@]}" "$WORK_DIR/"
 echo