message: add copy statement to ToString verification
diff: @@ -665,6 +665,7 @@ unique_ptr<PendingQueryResult> ClientContext::PendingStatementOrPreparedStatemen
  statement = std::move(copied_statement);
  break;
  }
  + case StatementType::COPY_STATEMENT:
  case StatementType::INSERT_STATEMENT:
  case StatementType::DELETE_STATEMENT:
  case StatementType::UPDATE_STATEMENT: {
  