Fix failures on Fedora.

Install rubygem-json RPM package in Fedora container as it is used in rake.

```
LoadError: cannot load such file -- json
/build/vendor/bundle/ruby/3.0.0/gems/rubocop-0.50.0/lib/rubocop/formatter/json_formatter.rb:3:in `require'
/build/vendor/bundle/ruby/3.0.0/gems/rubocop-0.50.0/lib/rubocop/formatter/json_formatter.rb:3:in `<top (required)>'
/build/vendor/bundle/ruby/3.0.0/gems/rubocop-0.50.0/lib/rubocop.rb:524:in `require'
/build/vendor/bundle/ruby/3.0.0/gems/rubocop-0.50.0/lib/rubocop.rb:524:in `<top (required)>'
/build/vendor/bundle/ruby/3.0.0/gems/rubocop-0.50.0/lib/rubocop/rake_task.rb:44:in `require'
/build/vendor/bundle/ruby/3.0.0/gems/rubocop-0.50.0/lib/rubocop/rake_task.rb:44:in `run_cli'
/build/vendor/bundle/ruby/3.0.0/gems/rubocop-0.50.0/lib/rubocop/rake_task.rb:36:in `run_main_task'
/build/vendor/bundle/ruby/3.0.0/gems/rubocop-0.50.0/lib/rubocop/rake_task.rb:28:in `block (2 levels) in initialize'
/build/vendor/bundle/ruby/3.0.0/gems/rubocop-0.50.0/lib/rubocop/rake_task.rb:26:in `block in initialize'
/build/vendor/bundle/ruby/3.0.0/gems/rake-13.0.3/exe/rake:27:in `<top (required)>'
```

Author: junaruga

ci/Dockerfile_fedora

@@ -20,6 +20,7 @@ RUN dnf -yq install \
   redhat-rpm-config \
   ruby-devel \
   rubygem-bigdecimal \
-  rubygem-bundler
+  rubygem-bundler \
+  rubygem-json
 
 CMD bash ci/container.sh