Bump puma from 5.6.4 to 5.6.7 in /backend (#654)

Bumps [puma](https://github.com/puma/puma) from 5.6.4 to 5.6.7.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](puma/puma@v5.6.4...v5.6.7)

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

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backend/Gemfile

@@ -17,7 +17,7 @@ gem "mongoid", "7.3.3"
 gem "pg", "1.2.3"
 
 # Use Puma as the app server
-gem "puma", "5.6.4"
+gem "puma", "5.6.7"
 
 # Authentication libraries
 gem "cancancan", "~> 3.3.0"

backend/Gemfile.lock

@@ -299,9 +299,9 @@ GEM
     pry-rails (0.3.9)
       pry (>= 0.10.4)
     public_suffix (5.0.3)
-    puma (5.6.4)
+    puma (5.6.7)
       nio4r (~> 2.0)
-    puma (5.6.4-java)
+    puma (5.6.7-java)
       nio4r (~> 2.0)
     pusher (2.0.2)
       httpclient (~> 2.8)
@@ -504,7 +504,7 @@ DEPENDENCIES
   pry-byebug
   pry-doc
   pry-rails
-  puma (= 5.6.4)
+  puma (= 5.6.7)
   pusher
   rack-cors (= 1.1.1)
   rack-timeout