chore: create a unique db for each parallel CI job

Author: ohmayr

.kokoro/system.sh

@@ -74,6 +74,9 @@ run_package_test() {
   export PROJECT_ID GOOGLE_APPLICATION_CREDENTIALS NOX_FILE NOX_SESSION
   export GOOGLE_CLOUD_PROJECT="${PROJECT_ID}"
 
+  # Give every parallel CI job a unique database so they don't clobber each other
+  export DJANGO_SPANNER_DB="db_${RANDOM}"
+
   gcloud auth activate-service-account --key-file="$GOOGLE_APPLICATION_CREDENTIALS"
   gcloud config set project "$PROJECT_ID"