tests: fix the out_stdout test ends before flushing
tests: fix the out_stdout test ends before flushing

takahasi/fluent-bit,nokute78/fluent-bit,nokute78/fluent-bit,nokute78/fluent-bit,nokute78/fluent-bit,nokute78/fluent-bit,fluent/fluent-bit,takahasi/fluent-bit,fluent/fluent-bit,fluent/fluent-bit,nokute78/fluent-bit,fluent/fluent-bit,fluent/fluent-bit,nokute78/fluent-bit,fluent/fluent-bit,takahasi/fluent-bit,fluent/fluent-bit,nokute78/fluent-bit,takahasi/fluent-bit,fluent/fluent-bit,nokute78/fluent-bit,takahasi/fluent-bit,takahasi/fluent-bit,fluent/fluent-bit,fluent/fluent-bit,nokute78/fluent-bit,fluent/fluent-bit,nokute78/fluent-bit,fluent/fluent-bit,nokute78/fluent-bit,takahasi/fluent-bit,takahasi/fluent-bit