Update deprecation notice for legacy alerts API (#9896)

* Update deprecation notice for legacy alerts API

Removed the removal date for the legacy alerts API.

* Revise legacy alerts deprecation notice

Updated deprecation notice for legacy alerts API and included a reference to the new alerts and incidents API.

* Apply suggestion from @FaithOmbongi

---------

Co-authored-by: Faith Moraa Ombongi <ombongi.moraa.fe@gmail.com>

Author: EdB-MSFT

api-reference/v1.0/includes/security-alerts-v1-deprecation.md

@@ -7,4 +7,4 @@ ms.topic: include
 
 <!-- markdownlint-disable MD041-->
 > [!NOTE]
-> The legacy alerts API is deprecated and will be removed by April 2026. We recommend that you migrate to the new [alerts and incidents](/graph/api/resources/security-alert) API.
+> The legacy alerts API is deprecated. We recommend that you migrate to the new [alerts and incidents](/graph/api/resources/security-alert) API.

api-reference/v1.0/resources/security-api-overview.md

@@ -90,8 +90,7 @@ Alerts from the following security providers are available via these rich alerts
 
 ### Legacy alerts
 
-> [!NOTE]
-> The legacy alerts API is deprecated and will be removed by April 2026. We recommend that you migrate to the new [alerts and incidents](/graph/api/resources/security-alert) API.
+[!INCLUDE [security-alerts-v1-deprecation](../includes/security-alerts-v1-deprecation.md)]
 
 The legacy [alert](alert.md) resources federate calling of supported Azure and Microsoft 365 Defender security providers. They aggregate common alert data among the different domains to allow applications to unify and streamline management of security issues across all integrated solutions. They enable applications to correlate alerts and context to improve threat protection and response.