If a contact has already subscribed to a Newsletter Group, do not send out confirmations if the user again signs up to that Newsletter Group

We have a Contribution page which displays the Contact, Group(s) field to allow users to sign-up for our Newsletters.

We noticed that if a user is already a member of a Newsletter Group and they submit another Contribution page that also selects the same Newsletter Group plus some additional ones.

That the contact then receives a email subscribe confirmations for BOTH the new and the existing group subscriptions. As selected on the Contribution Page.

It would be good if CiviCRM only sent the email subscribe confirmations for just the new groups. As the existing group memberships have already been confirmed.