How long can chickpeas soak in the fridge?

You'll know they've gone too long when lots of bubbles start appearing (indicating fermentation).

Yes, your refrigerated beans will be safe to cook and eat. Be sure to rinse them well and cook them in fresh water - not the salted soaking water, or they could end up too salty to eat. I would wait to add salt until after they have started to soften, and taste one first before deciding how much- if any- additional salt will be needed. In the future, if you'd like soaked beans on hand for quick use you can always freeze soaked beans in freezer zip bags so you don't have to worry about it. Frozen soaked beans can be simply added as is to fresh water and cooked without the need to thaw, and no worries that they may have started to ferment.