fix(data/equiv/set): Fix doc comment syntax (#11409)

src/data/equiv/set.lean

@@ -478,7 +478,7 @@ by { ext x, simp [(equiv.set.congr f).symm.exists_congr_left] }
 end equiv
 
 /-- If a function is a bijection between two sets `s` and `t`, then it induces an
-equivalence between the types `↥s` and ``↥t`. -/
+equivalence between the types `↥s` and `↥t`. -/
 noncomputable def set.bij_on.equiv {α : Type*} {β : Type*} {s : set α} {t : set β} (f : α → β)
   (h : set.bij_on f s t) : s ≃ t :=
 equiv.of_bijective _ h.bijective