Fix timetable preview

[takahirom]

Idea Description It is not possible at a real DroidKaigi for many sessions to run in parallel in the same room.

Reference images and links

We should fix the fake() logic

https://github.com/DroidKaigi/conference-app-2022/blob/1c152b630ac891dbfe5de0ff7c1b2e8244bc48bf/core-model/src/commonMain/kotlin/io/github/droidkaigi/confsched2022/model/Timetable.kt#L81

[surajsau]

I'll attempt it 🤚

[takahirom]

Thanks! Assigned 👍