chore: Improve checksum script

Suggested in #18483 (comment)

Author: spencergilbert

scripts/checksum.sh

@@ -13,10 +13,9 @@ VECTOR_VERSION=${VECTOR_VERSION:-nightly}
 pushd "${ROOT}/target/artifacts"
 
 shopt -s extglob
-ARTIFACTS=$(ls !(*SHA256SUMS))
+ARTIFACTS=(!(*SHA256SUMS))
 shopt -u extglob
 
-# shellcheck disable=SC2086 # Intended splitting of ARTIFACTS
-sha256sum $ARTIFACTS > vector-"$VECTOR_VERSION"-SHA256SUMS
+sha256sum "${ARTIFACTS[@]}" > vector-"$VECTOR_VERSION"-SHA256SUMS
 
 popd