Bharadwaj Raju authored May 05, 2021 and Nate Graham committed May 05, 2021

Previously the "clear clipboard history?" dialog used `KMessageBox::questionYesNo`
which if "don't ask again" is ticked then saves the answer even if No was answered.
This can cause the user to not be able to ever clear the clipboard ever again. This
commit changes it to `KMessageBox::warningContinueCancel` which doesn't do that, and
is more appropriate for the kind of question we're asking.

BUG: 336053
FIXED-IN: 5.22