ERT Guns can spawn with both a rail light and underbarrel light

### Testmerges

#10999, #11661, #11590

### Round ID

32643

### Description of the bug

Rail flashlights, underbarrel lights, and vertical grip lights, are all mutually exclusive with each other. Attempting to attach multiple will give you a prompt that says "you already have a light source attached".

When you spawn as an ERT member your gun bypasses that shit and you can get the Sun Stick 3000.

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

you shouldn't get 2 light sources

### How do we reproduce this bug?

1. roll for ERT
2. pray RNGesus gifts you with a double light MK2/2
3. blind xenos with the power of the sun (this does nothing)

### Issue Bingo

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