Auto merge of #104180 - fee1-dead-contrib:fix-wf-fndef, r=oli-obk

Use `nominal_obligations_without_const` in wf for FnDef

Fixes #104155.

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() {}