Bump puma from 5.6.4 to 5.6.9 in /demo

Bumps [puma](https://github.com/puma/puma) from 5.6.4 to 5.6.9.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](puma/puma@v5.6.4...v5.6.9)

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

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

demo/Gemfile.lock

@@ -8,11 +8,11 @@ GEM
     listen (3.7.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
-    nio4r (2.5.8)
+    nio4r (2.7.3)
     parallel (1.21.0)
     parser (3.0.3.1)
       ast (~> 2.4.1)
-    puma (5.6.4)
+    puma (5.6.9)
       nio4r (~> 2.0)
     rack (2.2.6.4)
     rack-test (1.1.0)