build(deps): bump puma from 4.3.12 to 5.6.8 in /ci/sinatra

Bumps [puma](https://github.com/puma/puma) from 4.3.12 to 5.6.8.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](puma/puma@v4.3.12...v5.6.8)

---
updated-dependencies:
- dependency-name: puma
  dependency-type: direct:production
...

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

ci/sinatra/Gemfile.lock

@@ -3,9 +3,9 @@ GEM
   specs:
     mustermann (2.0.2)
       ruby2_keywords (~> 0.0.1)
-    nio4r (2.5.8)
+    nio4r (2.7.0)
     pg (1.2.3)
-    puma (4.3.12)
+    puma (5.6.8)
       nio4r (~> 2.0)
     rack (2.2.6.4)
     rack-protection (2.2.3)