Fix system test for scaffolds

[siaw23]

Fixes #585

[xdmx]

Sending a bat-signal to @flavorjones as with the recent release of 8.1 this breaks scaffolds generations under it and it took me a minute to figure out that the reason was this gem (workaround: generate the system test with --system-tests=true)

[flavorjones]

Thanks for opening a pull request to try to fix this. Unfortunately, the integration test are still failing: https://github.com/rails/tailwindcss-rails/actions/runs/18120118719/job/51563116335?pr=586

I'll take a swing at fixing this now.

[flavorjones]

Closed in preference to #590

Thank you!!