ensure we only allow "left click"

A normal `click` handles that for you, but a mousedown does not. Let's
only allow a normal left click only.

Author: RobinMalfait

packages/@headlessui-react/src/components/listbox/listbox.tsx

@@ -394,6 +394,7 @@ function ButtonFn<TTag extends ElementType = typeof DEFAULT_BUTTON_TAG>(
   })
 
   let handleMouseDown = useEvent((event: ReactMouseEvent) => {
+    if (event.button !== 0) return // Only handle left clicks
     if (isDisabledReactIssue7711(event.currentTarget)) return event.preventDefault()
     if (machine.state.listboxState === ListboxStates.Open) {
       flushSync(() => machine.actions.closeListbox())

packages/@headlessui-react/src/components/menu/menu.tsx

@@ -230,6 +230,7 @@ function ButtonFn<TTag extends ElementType = typeof DEFAULT_BUTTON_TAG>(
   ])
 
   let handleMouseDown = useEvent((event: ReactMouseEvent) => {
+    if (event.button !== 0) return // Only handle left clicks
     if (isDisabledReactIssue7711(event.currentTarget)) return event.preventDefault()
     if (disabled) return
     if (menuState === MenuState.Open) {