Update ChainedBuilderExtensions.xml (#7849)

Correct typo in IConfigurationBuild summary: 'chaind' to 'chained'

Author: Nicholas Piazza

xml/Microsoft.Extensions.Configuration/ChainedBuilderExtensions.xml

@@ -20,7 +20,7 @@
   </Base>
   <Interfaces />
   <Docs>
-    <summary>IConfigurationBuilder extension methods for the chaind configuration provider.</summary>
+    <summary>IConfigurationBuilder extension methods for the chained configuration provider.</summary>
     <remarks>To be added.</remarks>
   </Docs>
   <Members>