Bump puma from 5.6.7 to 6.4.2 in /backend

Bumps [puma](https://github.com/puma/puma) from 5.6.7 to 6.4.2.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](puma/puma@v5.6.7...v6.4.2)

---
updated-dependencies:
- dependency-name: puma
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

backend/Gemfile

@@ -17,7 +17,7 @@ gem "mongoid", "7.3.3"
 gem "pg", "1.2.3"
 
 # Use Puma as the app server
-gem "puma", "5.6.7"
+gem "puma", "6.4.2"
 
 # Authentication libraries
 gem "cancancan", "~> 3.3.0"

backend/Gemfile.lock

@@ -246,8 +246,8 @@ GEM
       timeout
     net-smtp (0.4.0)
       net-protocol
-    nio4r (2.5.9)
-    nio4r (2.5.9-java)
+    nio4r (2.7.0)
+    nio4r (2.7.0-java)
     nokogiri (1.16.0)
       mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
@@ -295,9 +295,9 @@ GEM
     pry-rails (0.3.9)
       pry (>= 0.10.4)
     public_suffix (5.0.3)
-    puma (5.6.7)
+    puma (6.4.2)
       nio4r (~> 2.0)
-    puma (5.6.7-java)
+    puma (6.4.2-java)
       nio4r (~> 2.0)
     pusher (2.0.2)
       httpclient (~> 2.8)
@@ -500,7 +500,7 @@ DEPENDENCIES
   pry-byebug
   pry-doc
   pry-rails
-  puma (= 5.6.7)
+  puma (= 6.4.2)
   pusher
   rack-cors (= 2.0.1)
   rack-timeout