Fix missing add observer for password store observer
Fix missing add observer for password store observer

required by https://github.com/brave/browser-laptop/pull/9085

Auditors: 47e4a4954d6a66edd1210b9b46e0a144c1078e87@bbondy

brave/electron,brave/muon,brave/muon,brave/electron,brave/electron,brave/electron,brave/electron,brave/electron,brave/muon,brave/muon,brave/muon,brave/muon