Update migration-api-whats-new.md (SharePoint#8828)

Date change for SourceType requirement.

Author: JoanneHendrickson

docs/apis/migration-api-whats-new.md

@@ -1,7 +1,7 @@
 ---
 title: "Migration API What's new"
 description: "Learn about the new features and updates to the Migration API."
-ms.date: 11/20/2022
+ms.date: 03/20/2022
 ms.reviewer: jhendr
 author: JoanneHendrickson
 ms.author: jhendr
@@ -18,7 +18,7 @@ Check here to see what features or updates have been added to the Migration API.
 
 ## New requirement
 
-Beginning January 1, 2023, the SourceType field will be mandatory when calling the Migration API. Starting October 1st, 2022, a warning message will be sent if the field is missing.
+Beginning April 1, 2023, the SourceType field is mandatory when calling the Migration API. Starting October 1st, 2022, a warning message will be sent if the field is missing.
 
 To learn more, including examples, see: **[SharePoint Import Migration API - ExportSettings.xml](/sharepoint/dev/apis/migration-api-overview#exportsettingsxml)**