Suppress DEPRECATION warning in NetworkEventUtilTest (#56971)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/56971

The OSS build runs Kotlin with `-Werror`, and the test calls the now-deprecated overload `RequestBody.create(MediaType?, String)`. The file already suppresses `DEPRECATION_ERROR` for the same OkHttp-version skew; extend the existing `Silvochka:Suppress` to also cover the warning-level `DEPRECATION` so the build stops failing.

## Changelog:

[Internal]

Reviewed By: cortinico

Differential Revision: D106364355

fbshipit-source-id: fff61bbc0dec19e4d68b7a3c51262673587d904c