Fix XPF nuget config

(cherry picked from commit 39607c3)

Author: maxkatz6

samples/NuGet.config

@@ -21,7 +21,7 @@
   <packageSourceCredentials>
     <xpf>
       <add key="Username" value="license" />
-      <add key="ClearTextPassword" value="$(XpfLicenseKey)" />
+      <add key="ClearTextPassword" value="%XpfLicenseKey%" />
     </xpf>
   </packageSourceCredentials>
 </configuration>