build(deps): bump mini_racer from 0.9.0 to 0.12.0 in /docs/v3 (#3775)

Bumps [mini_racer](https://github.com/discourse/mini_racer) from 0.9.0 to 0.12.0.
- [Changelog](https://github.com/rubyjs/mini_racer/blob/main/CHANGELOG)
- [Commits](rubyjs/mini_racer@v0.9.0...v0.12.0)

---
updated-dependencies:
- dependency-name: mini_racer
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

docs/v3/Gemfile.lock

@@ -39,10 +39,10 @@ GEM
     json (2.7.2)
     kramdown (2.4.0)
       rexml
-    libv8-node (18.19.0.0)
-    libv8-node (18.19.0.0-arm64-darwin)
-    libv8-node (18.19.0.0-x86_64-darwin)
-    libv8-node (18.19.0.0-x86_64-linux)
+    libv8-node (21.7.2.0)
+    libv8-node (21.7.2.0-arm64-darwin)
+    libv8-node (21.7.2.0-x86_64-darwin)
+    libv8-node (21.7.2.0-x86_64-linux)
     listen (3.9.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
@@ -96,8 +96,8 @@ GEM
       middleman-core (>= 3.2)
       rouge (~> 1.0)
     mini_portile2 (2.8.6)
-    mini_racer (0.9.0)
-      libv8-node (~> 18.19.0.0)
+    mini_racer (0.12.0)
+      libv8-node (~> 21.7.2.0)
     minitest (5.22.3)
     nokogiri (1.16.4)
       mini_portile2 (~> 2.8.2)