build(deps): bump rack in /appengine/rails-cloudsql-mysql (#1540)

Bumps [rack](https://github.com/rack/rack) from 3.0.11 to 3.0.12.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](https://github.com/rack/rack/commits/v3.0.12)

---
updated-dependencies:
- dependency-name: rack
  dependency-type: indirect
...

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

Author: dependabot[bot]

appengine/rails-cloudsql-mysql/Gemfile.lock

@@ -228,7 +228,7 @@ GEM
     puma (6.3.1)
       nio4r (~> 2.0)
     racc (1.8.0)
-    rack (3.0.11)
+    rack (3.0.12)
     rack-session (2.0.0)
       rack (>= 3.0.0)
     rack-test (2.1.0)