ci: specify project id

Author: chingor13

.kokoro/build.sh

@@ -40,8 +40,9 @@ if [[ -f "${KOKORO_GFILE_DIR}/project-id.json" ]]
 then
   export PROJECT_ID=$(cat "${KOKORO_GFILE_DIR}/project-id.json")
 else
-  PROJECT_ID=precise-truck-742
+  export PROJECT_ID=precise-truck-742
 fi
+export GOOGLE_CLOUD_PROJECT="${PROJECT_ID}"
 
 # If this is a continuous build, send the test log to the FlakyBot.
 # See https://github.com/googleapis/repo-automation-bots/tree/main/packages/flakybot.