ASP-based solver: fix facts for default providers (#24380)

Facts used to compute weights for providers only need
the package name, since the other attributes are computed
as part of the solve.

lib/spack/spack/solver/asp.py

@@ -764,7 +764,8 @@ def virtual_preferences(self, pkg_name, func):
                 continue
 
             for i, provider in enumerate(providers):
-                func(vspec, provider, i + 10)
+                provider_name = spack.spec.Spec(provider).name
+                func(vspec, provider_name, i + 10)
 
     def provider_defaults(self):
         self.gen.h2("Default virtual providers")