Fix up partial res of segment in primitive resolution hack
There is a hack in the resolver:
```
// In `a(::assoc_item)*` `a` cannot be a module. If `a` does resolve to a module we
// don't report an error right away, but try to fallback to a primitive type.
```
This fixes up the resolution for primitives which would otherwise resolve to a module, but we weren't also updating the res of the path segment, leading to weird diagnostics.
We explicitly call `self.r.partial_res_map.insert` instead of `record_partial_res` b/c we have recorded a partial res already, and we specifically want to override it.
cc https://github.com/rust-lang/rust/issues/139095#issuecomment-2764371934
