Fixed errcheck issues in server/channels/app/group_test.go (#28938)

server/.golangci.yml

@@ -109,7 +109,6 @@ issues:
         channels/app/file_helper_test.go|\
         channels/app/file_info.go|\
         channels/app/file_test.go|\
-        channels/app/group_test.go|\
         channels/app/helper_test.go|\
         channels/app/imaging/decode.go|\
         channels/app/imaging/decode_test.go|\