Jumping into a van grants explosion immunity

### Testmerges

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### Round ID

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### Description of the bug

If you are in a van (maybe in other vehicles too?) you are fully immune to explosions from the outside. I am not sure if this qualifies as a "bug" since you are technically on a different z-level, but it is the same as jumping into a closet from explosions - I don't think you should get full immunity.

### What's the difference with what should have happened?

Whoever is inside should probably get a dampened amount of damage from explosions?

### How do we reproduce this bug?

1. Predator does a big SD
2. Van parks on top of them
3. Predator explodes
4. Van gets damaged somewhat, the guy inside is at 100% health

^ watched this in 4K HD today, I forgot the round ID

### Issue Bingo

- [ ] Issue could be reproduced at least once
- [X] Issue happened in a recent (less than 7 days ago) round
- [X] Couldn't find an existing issue about this (https://github.com/cmss13-devs/cmss13/issues)