Use nominal_obligations_without_const in wf for FnDef

compiler/rustc_trait_selection/src/traits/wf.rs

@@ -547,7 +547,7 @@ fn compute(&mut self, arg: GenericArg<'tcx>) {
                 }
 
                 ty::FnDef(did, substs) => {
-                    let obligations = self.nominal_obligations(did, substs);
+                    let obligations = self.nominal_obligations_without_const(did, substs);
                     self.out.extend(obligations);
                 }
 

src/test/ui/consts/issue-104155.rs

@@ -0,0 +1,5 @@
+// check-pass
+const _: () = core::mem::forget(Box::<u32>::default);
+const _: () = core::mem::forget(|| Box::<u32>::default());
+
+fn main() {}