Fix asset precompilation

[mamhoff]

What is this pull request for?

Fix asset precompilation in host apps with SassC in environments other than development. We were still using the old image-url Sass directive, whereas modern Sass/Sprockets can fingerprint assets referenced in URL directives directly.

Notable changes (remove if none)

Makes the current main branch deployable.

Screenshots

None :)

Checklist

• I have followed Pull Request guidelines
• I have added a detailed description into each commit message
• I have added tests to cover this change

[tvdeyen]

Thanks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.47%. Comparing base (a13577a) to head (15a79fd).
Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3024   +/-   ##
=======================================
  Coverage   96.47%   96.47%           
=======================================
  Files         237      237           
  Lines        6404     6404           
=======================================
  Hits         6178     6178           
  Misses        226      226           

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