Make it clear that args default to being related invariantly

compiler/rustc_infer/src/infer/equate.rs

@@ -56,7 +56,7 @@ impl<'tcx> TypeRelation<'tcx> for Equate<'_, '_, 'tcx> {
         // performing trait matching (which then performs equality
         // unification).
 
-        relate::relate_args(self, a_arg, b_arg)
+        relate::relate_args_invariantly(self, a_arg, b_arg)
     }
 
     fn relate_with_variance<T: Relate<'tcx>>(

compiler/rustc_infer/src/infer/generalize.rs

@@ -183,7 +183,7 @@ where
             // Avoid fetching the variance if we are in an invariant
             // context; no need, and it can induce dependency cycles
             // (e.g., #41849).
-            relate::relate_args(self, a_subst, b_subst)
+            relate::relate_args_invariantly(self, a_subst, b_subst)
         } else {
             let tcx = self.tcx();
             let opt_variances = tcx.variances_of(item_def_id);