Specify that the additional partial member field is optional

Author: lipfangmoe

docs/events/gateway-events.mdx

@@ -1001,7 +1001,7 @@ Sent when a message is created. The inner payload is a [message](/docs/resources
 |-----------|-------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------|
 | guild_id? | snowflake                                                                                                                                       | ID of the guild the message was sent in - unless it is an ephemeral message                            |
 | member?   | partial [guild member](/docs/resources/guild#guild-member-object) object                                                                        | Member properties for this message's author. Missing for ephemeral messages and messages from webhooks |
-| mentions  | array of [user](/docs/resources/user#user-object) objects, with an additional partial [member](/docs/resources/guild#guild-member-object) field | Users specifically mentioned in the message                                                            |
+| mentions  | array of [user](/docs/resources/user#user-object) objects, optionally with an additional partial [member](/docs/resources/guild#guild-member-object) field | Users specifically mentioned in the message                                                            |
 
 #### Message Update