scrolledwindow: Lower the scroll multiplier
c68247f6 introduced a scroll multiplier, intended to be significantly lower than the GTK 4.6 behavior but higher than 1. However, it was higher than 4.6, since 4.6 also had a permanent 1/10 multiplier in GDK, so the cited multiplier values were really 6.4 and 9.7.
A MR as per #4793 (comment 1521767)
Edited by Alice Mikhaylenko