doc: add missing YAML keyword in v8.md metadata

PR-URL: #20023
Reviewed-By: Yuta Hiroto <hello@hiroppy.me>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/v8.md

@@ -171,7 +171,7 @@ This API is under development, and changes (including incompatible
 changes to the API or wire format) may occur until this warning is removed.
 
 ### v8.serialize(value)
-<!--
+<!-- YAML
 added: v8.0.0
 -->
 
@@ -180,7 +180,7 @@ added: v8.0.0
 Uses a [`DefaultSerializer`][] to serialize `value` into a buffer.
 
 ### v8.deserialize(buffer)
-<!--
+<!-- YAML
 added: v8.0.0
 -->
 
@@ -190,7 +190,7 @@ Uses a [`DefaultDeserializer`][] with default options to read a JS value
 from a buffer.
 
 ### class: v8.Serializer
-<!--
+<!-- YAML
 added: v8.0.0
 -->
 
@@ -299,7 +299,7 @@ Indicate whether to treat `TypedArray` and `DataView` objects as
 host objects, i.e. pass them to [`serializer._writeHostObject()`][].
 
 ### class: v8.Deserializer
-<!--
+<!-- YAML
 added: v8.0.0
 -->
 
@@ -379,7 +379,7 @@ This method is not present on the `Deserializer` class itself but can be
 provided by subclasses.
 
 ### class: v8.DefaultSerializer
-<!--
+<!-- YAML
 added: v8.0.0
 -->
 
@@ -388,7 +388,7 @@ A subclass of [`Serializer`][] that serializes `TypedArray`
 stores the part of their underlying `ArrayBuffer`s that they are referring to.
 
 ### class: v8.DefaultDeserializer
-<!--
+<!-- YAML
 added: v8.0.0
 -->