doc(Algebra/BigOperators/Fin): change 'product' to 'sum' in doc-strin…

…g of additivised declarations (#21101)

The additivised declarations speak about sums: probably, this was a copy-paste error.

Mathlib/Algebra/BigOperators/Fin.lean

@@ -55,7 +55,7 @@ theorem prod_univ_zero [CommMonoid β] (f : Fin 0 → β) : ∏ i, f i = 1 :=
 /-- A product of a function `f : Fin (n + 1) → β` over all `Fin (n + 1)`
 is the product of `f x`, for some `x : Fin (n + 1)` times the remaining product -/
 @[to_additive "A sum of a function `f : Fin (n + 1) → β` over all `Fin (n + 1)` is the sum of
-`f x`, for some `x : Fin (n + 1)` plus the remaining product"]
+`f x`, for some `x : Fin (n + 1)` plus the remaining sum"]
 theorem prod_univ_succAbove [CommMonoid β] {n : ℕ} (f : Fin (n + 1) → β) (x : Fin (n + 1)) :
     ∏ i, f i = f x * ∏ i : Fin n, f (x.succAbove i) := by
   rw [univ_succAbove, prod_cons, Finset.prod_map _ x.succAboveEmb]
@@ -64,7 +64,7 @@ theorem prod_univ_succAbove [CommMonoid β] {n : ℕ} (f : Fin (n + 1) → β) (
 /-- A product of a function `f : Fin (n + 1) → β` over all `Fin (n + 1)`
 is the product of `f 0` plus the remaining product -/
 @[to_additive "A sum of a function `f : Fin (n + 1) → β` over all `Fin (n + 1)` is the sum of
-`f 0` plus the remaining product"]
+`f 0` plus the remaining sum"]
 theorem prod_univ_succ [CommMonoid β] {n : ℕ} (f : Fin (n + 1) → β) :
     ∏ i, f i = f 0 * ∏ i : Fin n, f i.succ :=
   prod_univ_succAbove f 0