function _startChild(transaction, { startTimestamp, ...ctx }) {
  // eslint-disable-next-line deprecation/deprecation
  if (startTimestamp && transaction.startTimestamp > startTimestamp) {
    // eslint-disable-next-line deprecation/deprecation
    transaction.startTimestamp = startTimestamp;
  }

  // eslint-disable-next-line deprecation/deprecation
  return transaction.startChild({
    startTimestamp,
    ...ctx,
  });
}
Helper function to start child on transactions. This function will make sure that the transaction will
use the start timestamp of the created child span if it is earlier than the transactions actual
start timestamp.

Note: this will not be possible anymore in v8,
unless we do some special handling for browser here...