Fixed errcheck issues in server/channels/app/file_bench_test.go (#29003)

Co-authored-by: Mattermost Build <build@mattermost.com>

server/.golangci.yml

@@ -92,7 +92,6 @@ issues:
         channels/app/brand.go|\
         channels/app/config_test.go|\
         channels/app/file.go|\
-        channels/app/file_bench_test.go|\
         channels/app/file_test.go|\
         channels/app/helper_test.go|\
         channels/app/import_functions.go|\