test(cdk/drag-drop): avoid flakes in scrolling tests (#23087)
test(cdk/drag-drop): avoid flakes in scrolling tests (#23087)

A recent change (#23026) appears to have introduced flakiness in our unit tests on Firefox. These changes apply a similar workaround to some of the other scrolling tests.
crisbeto/material2,mmalerba/material2,josephperrott/material2,angular/components,josephperrott/material2,josephperrott/material2,crisbeto/material2,mmalerba/material2,mmalerba/material2,angular/components,mmalerba/material2,angular/components,angular/components,josephperrott/material2,crisbeto/material2,crisbeto/material2,josephperrott/material2,mmalerba/material2