chore: relax typeclass assumption in Polynomial.support_smul (#10397)

Co-authored-by: Junyan Xu <junyanxu.math@gmail.com>

Mathlib/Data/Polynomial/Coeff.lean

@@ -58,7 +58,7 @@ theorem coeff_smul [SMulZeroClass S R] (r : S) (p : R[X]) (n : ℕ) :
   exact Finsupp.smul_apply _ _ _
 #align polynomial.coeff_smul Polynomial.coeff_smul
 
-theorem support_smul [Monoid S] [DistribMulAction S R] (r : S) (p : R[X]) :
+theorem support_smul [SMulZeroClass S R] (r : S) (p : R[X]) :
     support (r • p) ⊆ support p := by
   intro i hi
   simp? [mem_support_iff] at hi ⊢ says simp only [mem_support_iff, coeff_smul, ne_eq] at hi ⊢