fix(compute): ensure trailing newline in fetched discovery doc (#16407)

Author: colinmoy

generator/discovery/update_discovery_doc.sh

@@ -101,6 +101,11 @@ if ! curl -fsSL "${COMPUTE_DISCOVERY_DOCUMENT_URL}" >"${TEMP_JSON}"; then
   exit 1
 fi
 
+# Ensure the discovery document ends with a trailing newline.
+if [[ -s "${TEMP_JSON}" && -n "$(tail -c 1 "${TEMP_JSON}")" ]]; then
+  echo >>"${TEMP_JSON}"
+fi
+
 REVISION=$(sed -En 's/  \"revision\": \"([[:digit:]]+)\",/\1/p' "${TEMP_JSON}")
 if [[ -z "${REVISION}" ]]; then
   io::log_red "Could not parse revision from fetched discovery document."