Bump oj from 3.7.7 to 3.7.8 (mastodon#9900)

Bumps [oj](https://github.com/ohler55/oj) from 3.7.7 to 3.7.8.
- [Release notes](https://github.com/ohler55/oj/releases)
- [Changelog](https://github.com/ohler55/oj/blob/master/CHANGELOG.md)
- [Commits](ohler55/oj@v3.7.7...v3.7.8)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Gemfile.lock

@@ -363,7 +363,7 @@ GEM
       concurrent-ruby (~> 1.0, >= 1.0.2)
       sidekiq (>= 3.5)
       statsd-ruby (~> 1.4, >= 1.4.0)
-    oj (3.7.7)
+    oj (3.7.8)
     omniauth (1.9.0)
       hashie (>= 3.4.6, < 3.7.0)
       rack (>= 1.6.2, < 3)