Suppress warning using different secondary for out_secondary_file

[daipom]

Which issue(s) this PR fixes:
None.

What this PR does / why we need it:
Fluentd outputs the following warning message even when we use out_secondary_file for the secondary.

2023-03-09 14:50:10 +0900 [warn]: #0 Use different plugin for secondary. Check the plugin works with primary like secondary_file primary="Fluent::Plugin::FileOutput" secondary="Fluent::Plugin::SecondaryFileOutput"

Example config:

<source>
  @type sample
  tag test.hoge
  sample {"message": "hoge"}
</source>

<match test.**>
  @type file
  path /test/fluentd/log/${tag}/fluentd.log
  <format>
    @type single_value
  </format>
  <buffer tag>
    @type file
    path /test/fluentd/buffer
    flush_mode interval
    flush_interval 10s
  </buffer>
  <secondary>
    @type secondary_file
    directory /test/fluentd/error/
  </secondary>
</match>

This warning is meaningless when we use out_secondary_file for the secondary.

This PR suppresses it.

Docs Changes:
Not needed.

Release Note:
Same as the title.

[ashie]

Thanks!

[daipom]

Thanks for your review!