docs: capitalize List.All in it's own docstring (#7784)

Mathlib/Data/List/Defs.lean

@@ -220,7 +220,7 @@ end mapIdxM
 #align list.sublists List.sublists
 #align list.forall₂ List.Forall₂
 
-/-- `l.all₂ p` is equivalent to `∀ a ∈ l, p a`, but unfolds directly to a conjunction, i.e.
+/-- `l.All₂ p` is equivalent to `∀ a ∈ l, p a`, but unfolds directly to a conjunction, i.e.
 `List.All₂ p [0, 1, 2] = p 0 ∧ p 1 ∧ p 2`. -/
 @[simp]
 def All₂ (p : α → Prop) : List α → Prop