Previously we assumed that all unlifted types were `Addr#` but this
isn't true. As noted in #25638, unlifted nullary data constructor
workers can also appear at the top-level and are obviously not of type
`Addr#`.

Note that there is more work to be done to properly handle unlifted data
constructors (especially nullary; see #25636). However, this is a small
step in the right direction.

Closes #25641.