Use plural form for packages & registries settings alerts

The following discussion from !103025 (merged) should be addressed:

• @zcuddy started a discussion:

  thought (non-blocking): At first glance passing the 2 to this method felt a bit like a magic number. Looking at it some more I see that it is existing logic to decide whether to be singular or plural in the message.

  It does make me wonder if we could get away with using the plural option always since all the components are named in a plural form. This is a bit of a bike shed comment it just really caught my eye. No action needed but we could open a follow up if you agree with the note.