fix(cdk/drag-drop): add conditional to scroll update

[andrewseguin]

Fix proposed by internal user to fix an issue with dragging. Open for discussion on whether this fix is valid.

[crisbeto]

What issue is this supposed to fix? The idea with this block of code is to update the cached dimensions whenever something within the container is scrolled. I think that would be valid when the container itself is scrolled too.

[andrewseguin]

When dragging an item in a list where there's a scrollbar, the item gets stuck in place while the list scrolls.

Here's a reproduction: #23337

You'll have to copy/paste the reproduction into the dev-app to see it against the latest changes.

[crisbeto]

LGTM

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