Do not allow migration for read-only config

Right?

Author: helje5

Sources/ManagedModels/Container/NSPersistentStoreDescription+Data.swift

@@ -24,6 +24,10 @@ extension NSPersistentStoreDescription {
 
     // TBD: options, timeout, sqlitePragmas
 
+    if !modelConfiguration.allowsSave {
+      shouldMigrateStoreAutomatically = false
+    }
+    
     shouldAddStoreAsynchronously = false
     // shouldMigrateStoreAutomatically
     // shouldInferMappingModelAutomatically