mlog standardisation for app/import.go (#12741)

* mlog standardisation for app/import.go

* using the corrent mlog.Field type for the error

app/import.go

@@ -6,7 +6,6 @@ package app
 import (
 	"bufio"
 	"encoding/json"
-	"fmt"
 	"io"
 	"net/http"
 	"strings"
@@ -19,7 +18,7 @@ import (
 
 func stopOnError(err LineImportWorkerError) bool {
 	if err.Error.Id == "api.file.upload_file.large_image.app_error" {
-		mlog.Warn(fmt.Sprintf("Large image import error: %s", err.Error.Error()))
+		mlog.Warn("Large image import error", mlog.Err(err.Error))
 		return false
 	}
 	return true