The answer is that this part of the journal doesn’t have to be published. The Journals clause also provides: “Each House shall keep a Journal of its Proceedings, and from time to time publish the same, excepting such Parts as may in their Judgment require Secrecy.”
The Senate could, by amending its rules, decide that when it acts as a jury of impeachment, its deliberations and its vote may be recorded in the journal but nonetheless require secrecy, in the same manner that criminal petit jury’s deliberations and individual votes remain.
And the Senate can amend its rules by majority vote.
*remain secret
