Can scroll sidebar while dragging it closed

### Expected

I expect to be able to _either_ scroll the sidebar up/down or drag the sidebar open/closed.

### Observed

I can scroll the sidebar up/down _while_ I drag the sidebar open/closed. This only happens when I start both actions at the same time. (If I scroll first and then try to drag, or drag first and then try to scroll, it doesn't happen.)

### Reproduced

1. Open the sidebar.
2. Swipe at a diagonal that starts a sideways motion and an up or down motion at the same time. This starts both the scroll and swipe-to-close actions simultaneously.
3. Continue holding your finger down as you scroll up/down or drag left/right, and note that both actions happen.


Make|Model|iOS Version|App Version
-|-|-|-
Apple|iPad Mini|13.1.2|4.12.0.1 beta

Start by reproducing the diagonal swipe on the iPad sidebar described in the issue, using the listed iOS and app versions if available. Trace the sidebar's scroll and swipe-to-close entry points, then verify that a diagonal gesture activates only one action rather than both.

Written by the indexing model from the issue text.