fix: name collision on Countable.toSmall (#11914)

This is currently causing mathport to fail, it's a new kind of name collision that has not occurred before: two definitions made in two different files are being `#align`ed to the same thing. Normally mathport will automatically rename one of them but in this case neither one imports the other so it doesn't know to avoid the situation.



Co-authored-by: Mario Carneiro <di.gama@gmail.com>

Mathlib/Data/Countable/Small.lean

@@ -22,7 +22,7 @@ instance (priority := 100) Countable.toSmall (α : Type v) [Countable α] : Smal
   let ⟨_, hf⟩ := exists_injective_nat α
   small_of_injective hf
 #align small_of_countable Countable.toSmall
-#align small_of_fintype Countable.toSmall
+#align small_of_fintype Countable.toSmallₓ -- this alignment clashes with the one above
 
 @[deprecated, nolint defLemma] -- 2024-03-20
 alias small_of_countable := Countable.toSmall