Fix Errcheck issues in server/channels/api4/export.go (#28407)

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

server/.golangci.yml

@@ -74,7 +74,6 @@ issues:
         channels/api4/config_local.go|\
         channels/api4/config_test.go|\
         channels/api4/data_retention.go|\
-        channels/api4/export.go|\
         channels/api4/export_test.go|\
         channels/api4/file_test.go|\
         channels/api4/import_test.go|\