Fix platform error when running tests on GitHub

The error was:

Your bundle only supports platforms ["arm64-darwin-23"] but your local platform
is x86_64-linux. Add the current platform to the lockfile with
`bundle lock --add-platform x86_64-linux` and try again.
Error: The process '/opt/hostedtoolcache/Ruby/3.2.2/x64/bin/bundle' failed with exit code 16

Gemfile.lock

@@ -35,6 +35,8 @@ GEM
     much-stub (0.1.10)
     nokogiri (1.15.5-arm64-darwin)
       racc (~> 1.4)
+    nokogiri (1.15.5-x86_64-linux)
+      racc (~> 1.4)
     parallel (1.23.0)
     parser (3.2.2.4)
       ast (~> 2.4.1)
@@ -112,6 +114,7 @@ GEM
 
 PLATFORMS
   arm64-darwin-23
+  x86_64-linux
 
 DEPENDENCIES
   benchmark-ips