replay: #3604 for MonoidAlgebra (#12646)

Weaken a couple of `DistribSMul` to `SMulZero` in `MonoidAlgebra`.

This parallels the analogous assumptions in the `AddMonoidAlgebra` instances that were weakened in #3604.

Found in the context of unifying `AddMonoidAlgebra` and `MonoidAlgebra`.

Mathlib/Algebra/MonoidAlgebra/Basic.lean

@@ -386,8 +386,8 @@ instance module [Semiring R] [Semiring k] [Module R k] : Module R (MonoidAlgebra
   Finsupp.module G k
 #align monoid_algebra.module MonoidAlgebra.module
 
-instance faithfulSMul [Monoid R] [Semiring k] [DistribMulAction R k] [FaithfulSMul R k]
-    [Nonempty G] : FaithfulSMul R (MonoidAlgebra k G) :=
+instance faithfulSMul [Semiring k] [SMulZeroClass R k] [FaithfulSMul R k] [Nonempty G] :
+    FaithfulSMul R (MonoidAlgebra k G) :=
   Finsupp.faithfulSMul
 #align monoid_algebra.has_faithful_smul MonoidAlgebra.faithfulSMul
 
@@ -396,12 +396,12 @@ instance isScalarTower [Semiring k] [SMulZeroClass R k] [SMulZeroClass S k] [SMu
   Finsupp.isScalarTower G k
 #align monoid_algebra.is_scalar_tower MonoidAlgebra.isScalarTower
 
-instance smulCommClass [Monoid R] [Monoid S] [Semiring k] [DistribMulAction R k]
-    [DistribMulAction S k] [SMulCommClass R S k] : SMulCommClass R S (MonoidAlgebra k G) :=
+instance smulCommClass [Semiring k] [SMulZeroClass R k] [SMulZeroClass S k] [SMulCommClass R S k] :
+    SMulCommClass R S (MonoidAlgebra k G) :=
   Finsupp.smulCommClass G k
 #align monoid_algebra.smul_comm_tower MonoidAlgebra.smulCommClass
 
-instance isCentralScalar [Monoid R] [Semiring k] [DistribMulAction R k] [DistribMulAction Rᵐᵒᵖ k]
+instance isCentralScalar [Semiring k] [SMulZeroClass R k] [SMulZeroClass Rᵐᵒᵖ k]
     [IsCentralScalar R k] : IsCentralScalar R (MonoidAlgebra k G) :=
   Finsupp.isCentralScalar G k
 #align monoid_algebra.is_central_scalar MonoidAlgebra.isCentralScalar