Relax subG mode

With Coq master, we otherwise fail to infer instances with subG_savedAnythingΣ, which leads to goals like

> looking for (subG
>                       (@savedAnythingΣ (@ofe_funCF val (fun _ : val => laterCF idCF))
>                          ?cFunctorContractive0) Σ)

theories/base_logic/lib/iprop.v

@@ -87,7 +87,7 @@ search is only triggered if the arguments of [subG] do not contain evars. Since
 instance search for [subG] is restrained, instances should persistently have [subG] as
 their first parameter to avoid loops. For example, the instances [subG_authΣ]
 and [auth_discrete] otherwise create a cycle that pops up arbitrarily. *)
-Hint Mode subG + + : typeclass_instances.
+Hint Mode subG ! + : typeclass_instances.
 
 Lemma subG_inv Σ1 Σ2 Σ : subG (gFunctors.app Σ1 Σ2) Σ → subG Σ1 Σ * subG Σ2 Σ.
 Proof.