Bump puma from 4.3.5 to 4.3.8 in /examples/ruby/backend (#5864)

Bumps [puma](https://github.com/puma/puma) from 4.3.5 to 4.3.8.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](puma/puma@v4.3.5...v4.3.8)

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

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

Author: dependabot[bot]

examples/ruby/backend/Gemfile.lock

@@ -1,8 +1,8 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    nio4r (2.5.2)
-    puma (4.3.5)
+    nio4r (2.5.7)
+    puma (4.3.8)
       nio4r (~> 2.0)
     rack (2.1.4)
     rack-unreloader (1.7.0)