Update codeowners (Azure#50768)

Author: JoshLove-msft

.github/CODEOWNERS

@@ -1198,7 +1198,7 @@
 # ######## Code Generation ########
 
 #PRLabel: %CodeGen %Client
-/eng/packages/http-client-csharp/                                  @JoshLove-msft @m-nash @jorgerangel-msft @live1206 @ArcturusZhang @jsquire
+/eng/packages/http-client-csharp/                                  @JoshLove-msft @m-nash @jorgerangel-msft @live1206 @ArcturusZhang @jsquire @christothes
 
 #PRLabel: %CodeGen %Mgmt
 /eng/packages/http-client-csharp-mgmt/                             @JoshLove-msft @m-nash @jorgerangel-msft @live1206 @ArcturusZhang