Bump rack from 3.1.12 to 3.1.16 in /examples/unicorn

Bumps [rack](https://github.com/rack/rack) from 3.1.12 to 3.1.16.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](rack/rack@v3.1.12...v3.1.16)

---
updated-dependencies:
- dependency-name: rack
  dependency-version: 3.1.16
  dependency-type: indirect
...

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

Author: dependabot[bot]

examples/unicorn/gems.locked

@@ -76,7 +76,7 @@ GEM
     protocol-rack (0.11.2)
       protocol-http (~> 0.43)
       rack (>= 1.0)
-    rack (3.1.12)
+    rack (3.1.16)
     raindrops (0.20.1)
     samovar (2.3.0)
       console (~> 1.0)