update time travel comment

bqetl_project.yaml

@@ -42,7 +42,7 @@ dry_run:
   - sql/moz-fx-data-shared-prod/accounts_backend_external/nonprod_emails_v1/query.sql
   - sql/moz-fx-data-shared-prod/accounts_backend_external/accounts_v1/query.sql
   - sql/moz-fx-data-shared-prod/accounts_backend_external/emails_v1/query.sql
-  # uses time travel, will error on current date
+  # uses time travel, will error on dates prior to the time travel window
   - sql/moz-fx-data-shared-prod/accounts_backend_derived/monitoring_db_counts_v1/query.sql
   - sql/moz-fx-data-shared-prod/accounts_db_external/**/*.sql
   - sql/moz-fx-data-shared-prod/accounts_db_nonprod_external/**/*.sql