bundle lock --add-platform x86_64-linux

My GitHub action was failing. The error message was:

> Your bundle only supports platforms ["arm64-darwin-22"] 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.

I followed the instructions in the error message. This should do it.

Gemfile.lock

@@ -25,9 +25,6 @@ GEM
       kramdown (~> 2.0)
     minitest (5.20.0)
     mutex_m (0.2.0)
-    nokogiri (1.15.5-arm64-darwin)
-      racc (~> 1.4)
-    racc (1.7.3)
     rake (13.1.0)
     rexml (3.2.6)
     rouge (4.2.0)
@@ -41,13 +38,13 @@ GEM
 
 PLATFORMS
   arm64-darwin-22
+  x86_64-linux
 
 DEPENDENCIES
   activesupport
   kramdown
   kramdown-parser-gfm
   minitest
-  nokogiri
   rake
   rouge
   rss