Fix sandbox command for Rails 8

[tvdeyen]

Summary

Rails 8 does not create a sprockets manifest anymore, but we still depend on it. Since rails commands do not work anymore, because sprockets raises an error if no manifest.js file is present we need to create it in order to be able to run rails new

Checklist

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.81%. Comparing base (4a892c3) to head (a7f0011).
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6133   +/-   ##
=======================================
  Coverage   88.81%   88.81%           
=======================================
  Files         835      835           
  Lines       18146    18146           
=======================================
  Hits        16116    16116           
  Misses       2030     2030           

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[kennyadsl]

Thanks @tvdeyen! Do we need this here as well?

[tvdeyen]

Thanks @tvdeyen! Do we need this here as well?

Yes, it's done in solidusio/solidus_dev_support@1949ffc