Correct test logic in QrCodeScannerControllerTest

This changelist updates test code to mirror production code for how
settings values are stored and retrieved. Settings written as
int/string should only be read as int/string respectively.

Test: atest QRCodeScannerControllerTest
Flag: EXEMPT bugfix
Bug: 402551650
Change-Id: If0d3d94255f125f00572eb27193038ca4af70903