Build(deps): Bump mini_racer from 0.2.14 to 0.2.15 (#10142)

Bumps [mini_racer](https://github.com/discourse/mini_racer) from 0.2.14 to 0.2.15.
- [Release notes](https://github.com/discourse/mini_racer/releases)
- [Changelog](https://github.com/rubyjs/mini_racer/blob/master/CHANGELOG)
- [Commits](https://github.com/discourse/mini_racer/compare/v0.2.14...v0.2.15)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Gemfile.lock

@@ -188,7 +188,7 @@ GEM
     method_source (1.0.0)
     mini_mime (1.0.2)
     mini_portile2 (2.4.0)
-    mini_racer (0.2.14)
+    mini_racer (0.2.15)
       libv8 (> 7.3)
     mini_scheduler (0.12.2)
       sidekiq