Update cssbundling-rails to resolve redundant Yarn install

[aduth]

🛠 Summary of changes

Updates cssbundling-rails gem dependency to the latest version, from 1.0.0 to 1.4.0.

This resolves an issue where yarn install would be called redundantly during deployments and in continuous integration during the assets:precompile task. We intend to skip Yarn install during this task in both continuous integration (source) and deploys (source) since it is done as part of a previous step (source, source). However, both jsbundling-rails and cssbundling-rails both include a built-in yarn install, and while the environment variable was enough to prevent the install in jsbundling-rails, it was not supported as of the version of cssbundling-rails we had installed previously. This was identified via troubleshooting at rails/jsbundling-rails#150 (comment), and is supported as of cssbundling-rails@1.3.0.

📜 Testing Plan

1. Run SKIP_YARN_INSTALL=true rails assets:precompile
2. Verify that the first command you see is yarn run and not yarn install

[aduth]

Also verified in GitLab builds for this pull request:

Before:

...
$ bundle exec rake assets:precompile
yarn install v1.22.19
...

After:

$ bundle exec rake assets:precompile
yarn run v1.22.19
...