[MM-61103] Fix errcheck issues in server/channels/app/channel_category_test.go (#28790)

Co-authored-by: Ben Schumacher <ben.schumacher@mattermost.com>

server/.golangci.yml

@@ -98,7 +98,6 @@ issues:
         channels/app/busy_test.go|\
         channels/app/channel.go|\
         channels/app/channel_bookmark_test.go|\
-        channels/app/channel_category_test.go|\
         channels/app/channel_test.go|\
         channels/app/config_test.go|\
         channels/app/desktop_login.go|\