Update Cloud Shell contact (#36439)

Author: mccoyp

.github/CODEOWNERS

@@ -522,7 +522,7 @@
 #/<NotInRepo>/          @sgellock
 
 # ServiceLabel: %Cloud Shell %Service Attention
-#/<NotInRepo>/          @maertendMSFT
+#/<NotInRepo>/          @mbifeld
 
 # ServiceLabel: %Cognitive - Custom Vision %Service Attention
 #/<NotInRepo>/          @areddish @tburns10