QTree is missing the lazy-loading icon and does not fire the onlazyload event

[HayasyLL]

Describe the bug
QTree is missing the lazy-loading icon and does not fire the onlazyload event

Codepen/jsFiddle/Codesandbox (required)
The error is even in the Doc sample: https://next.quasar.dev/vue-components/tree#Lazy-loading

To Reproduce
Steps to reproduce the behavior:

1. Go to 'https://next.quasar.dev/vue-components/tree#Lazy-loading
2. See error

Expected behavior
show lazy-loading icon and fire event

Screenshots

Platform (please complete the following information):
Quasar Version: v2.0.0-beta.3
@quasar/app Version:
Quasar mode:
[ ] SPA
[ ] SSR
[ ] PWA
[ ] Electron
[ ] Cordova
[ ] Capacitor
[ ] BEX
Tested on:
[ ] SPA
[ ] SSR
[ ] PWA
[ ] Electron
[ ] Cordova
[ ] Capacitor
[ ] BEX
OS:
Node:
NPM:
Yarn:
Browsers:
iOS:
Android:
Electron:

Additional context

[rstoenescu]

Fix will be available in Quasar 2.0.0-beta.4.