snack-bar-container.ts throws error on liveElement

[OlivierAlbertini]

To reproduce the issue : run stories related to snackBar
identified here https://github.com/VilledeMontreal/angular-ui/pull/192/files
Throw error since the implementation (Angular 15) : https://services.montreal.ca/bao-storybook/ <--- it's storybook 6 with Angular 15 for now)