Use sassc-embeded to compile Sass

To do: see if we can configure to silence warning

Built-in sassc compiler doesn't compile
stylesheet do to them, containing source maps

https://github.com/sass-contrib/sassc-embedded-shim-ruby

govuk_tech_docs.gemspec

@@ -53,6 +53,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency "openapi3_parser", "~> 0.9.0"
   spec.add_dependency "redcarpet", "~> 3.6"
   spec.add_dependency "terser", "~> 1.2.3"
+  spec.add_dependency "sassc-embedded", "~> 1.78.0"
 
   spec.add_development_dependency "byebug"
   spec.add_development_dependency "capybara", "~> 3.32"

lib/govuk_tech_docs.rb

@@ -11,6 +11,7 @@
 require "chronic"
 require "active_support/all"
 require "terser"
+require "sassc-embedded"
 
 require "govuk_tech_docs/redirects"
 require "govuk_tech_docs/table_of_contents/helpers"
@@ -51,6 +52,9 @@ def self.configure(context, options = {})
                 tables: true,
                 no_intra_emphasis: true
 
+    # this doesnt seem to work
+    context.set :sass, { output_style: "nested", quiet_deps: true }
+
     # Reload the browser automatically whenever files change
     context.configure :development do
       activate :livereload, options[:livereload].to_h