chore: restore @[simp] on Array.swapAt!_def

src/Init/Data/Array/Lemmas.lean

@@ -481,7 +481,7 @@ theorem get?_swap (a : Array α) (i j : Fin a.size) (k : Nat) : (a.swap i j)[k]?
 @[simp] theorem swapAt_def (a : Array α) (i : Fin a.size) (v : α) :
     a.swapAt i v = (a[i.1], a.set i v) := rfl
 
--- @[simp] -- FIXME: gives a weird linter error
+@[simp]
 theorem swapAt!_def (a : Array α) (i : Nat) (v : α) (h : i < a.size) :
     a.swapAt! i v = (a[i], a.set ⟨i, h⟩ v) := by simp [swapAt!, h]