React 19 compatibility: update to `react-dnd-multi-backend` version 9

[fengelniederhammer]

Could you please update the dependency? The current version of react-dnd-multi-backend (8.0.0) only allows React 18.

(related to #217)

[sanderdesnaijer]

Opened a PR #239 here to fix this issue including updating to React 19

[Lonli-Lokli]

You can also try my fork
https://www.npmjs.com/package/@lonli-lokli/react-mosaic-component