Fix typo in track 2 migration guide (Azure#14006)

* Fix typo in track 2 migration guide

* Update python_mgmt_migration_guide.rst

Author: nickzhums

doc/sphinx/python_mgmt_migration_guide.rst

@@ -102,7 +102,7 @@ To the show the code snippets for the change:
     from azure.identity import ClientSecretCredential
 
     credential = ClientSecretCredential(
-        tenant_id=tenant_id,
+        client_secret=client_secret,
         client_id=client_id,
         tenant_id=tenant_id
     )
@@ -167,3 +167,4 @@ If you have encountered an issue during migration, please file an issue
 via `Github
 Issues <https://github.com/Azure/azure-sdk-for-python/issues>`__ and
 make sure you add the "Preview" label to the issue
+