Bump puma from 5.6.2 to 5.6.4 in /playbook-website (#1829)

Bumps [puma](https://github.com/puma/puma) from 5.6.2 to 5.6.4.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](puma/puma@v5.6.2...v5.6.4)

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

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

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

playbook-website/Gemfile

@@ -10,7 +10,7 @@ gem "playbook_ui", path: "../playbook"
 # Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
 gem "rails", "~> 5.2.4", ">= 5.2.4.4"
 # Use Puma as the app server
-gem "puma", "~> 5.5"
+gem "puma", "~> 5.6"
 gem "slim-rails", "~> 3.2"
 # Transpile app-like JavaScript. Read more: https://github.com/rails/webpacker
 gem "webpacker", "4.3.0"

playbook-website/Gemfile.lock

@@ -122,7 +122,7 @@ GEM
     parser (3.0.3.2)
       ast (~> 2.4.1)
     public_suffix (4.0.6)
-    puma (5.6.2)
+    puma (5.6.4)
       nio4r (~> 2.0)
     racc (1.5.2)
     rack (2.2.3)
@@ -247,7 +247,7 @@ DEPENDENCIES
   health_check
   listen (>= 3.0.5, < 3.7.2)
   playbook_ui!
-  puma (~> 5.5)
+  puma (~> 5.6)
   rails (~> 5.2.4, >= 5.2.4.4)
   rubocop (= 1.23.0)
   rubocop-performance (~> 1.11.5)