Update ms.subservic for Entra ExtID invitation APIs

Author: FaithOmbongi

api-reference/v1.0/resources/invitation.md

@@ -3,7 +3,7 @@ title: "invitation resource type"
 description: "Represents an invitation that is used to add external users to an organization as part of Microsoft Entra business-to-business (Microsoft Entra B2B) collaboration."
 ms.localizationpriority: high
 author: "ppolkadots"
-ms.subservice: "entra-sign-in"
+ms.subservice: "entra-users"
 doc_type: resourcePageType
 ms.date: 06/05/2024
 ---