Update oj requirement from 3.16.7 to 3.16.8

Updates the requirements on [oj](https://github.com/ohler55/oj) to permit the latest version.
- [Release notes](https://github.com/ohler55/oj/releases)
- [Changelog](https://github.com/ohler55/oj/blob/develop/CHANGELOG.md)
- [Commits](ohler55/oj@v3.16.7...v3.16.8)

---
updated-dependencies:
- dependency-name: oj
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile

@@ -11,4 +11,4 @@ gem 'fluent-plugin-multi-format-parser', '1.1.0'
 gem 'fluent-plugin-opensearch', '1.0.10'
 gem 'fluent-plugin-prometheus', '2.2.0'
 gem 'fluent-plugin-systemd', '1.1.0'
-gem 'oj', '3.16.7'
+gem 'oj', '3.16.8'