fix: make isFailedOver non-nullable to resolve schema validation warning

Address Schema.Validation.NullableBooleanShouldBeEnum by adding Nullable='false'
to the isFailedOver property on cloudPC entity. The property only has two states
(true/false), so nullable is not needed.

Author: ms-linxin

schemas/beta-Prod.csdl

@@ -26150,7 +26150,7 @@
         <Property Name="displayName" Type="Edm.String" />
         <Property Name="frontlineCloudPcAvailability" Type="graph.frontlineCloudPcAvailability" />
         <Property Name="gracePeriodEndDateTime" Type="Edm.DateTimeOffset" />
-        <Property Name="isFailedOver" Type="Edm.Boolean" />
+        <Property Name="isFailedOver" Type="Edm.Boolean" Nullable="false" />
         <Property Name="groupDetail" Type="graph.cloudPcEntraGroupDetail" />
         <Property Name="imageDisplayName" Type="Edm.String" />
         <Property Name="lastLoginResult" Type="graph.cloudPcLoginResult" />