Mark preference property used in reflection as keep in Proguard

'notificationsPermissionRequested' property in PrefsRepository was
used with reflection but it was not marked in Proguard to be kept.

This was crashing the login system.

Author: lukstbit

AnkiDroid/proguard-rules.pro

@@ -29,6 +29,7 @@
 -keep class androidx.core.app.ActivityCompat$* { *; }
 -keep class androidx.concurrent.futures.** { *; }
 -keep class androidx.appcompat.view.menu.MenuItemImpl { *; } # .utils.ext.MenuItemImpl
+-keep class com.ichi2.anki.settings.PrefsRepository { *; } # PrefsRepository.notificationsPermissionRequested
 
 # Ignore unused packages
 -dontwarn javax.naming.**