DEV: Change method used to reference custom font assets (#13446)

The `asset-url` helper has been deprecated.

lib/stylesheet/importer.rb

@@ -213,8 +213,9 @@ module Stylesheet
       contents = +""
 
       if font[:variants].present?
+        fonts_dir = UrlHelper.absolute("#{Discourse.base_path}/fonts")
         font[:variants].each do |variant|
-          src = variant[:src] ? variant[:src] : "asset-url(\"/fonts/#{variant[:filename]}?v=#{DiscourseFonts::VERSION}\") format(\"#{variant[:format]}\")"
+          src = variant[:src] ? variant[:src] : "url(\"#{fonts_dir}/#{variant[:filename]}?v=#{DiscourseFonts::VERSION}\") format(\"#{variant[:format]}\")"
           contents << <<~EOF
             @font-face {
               font-family: #{font[:name]};

spec/components/stylesheet/importer_spec.rb

@@ -61,6 +61,13 @@ describe Stylesheet::Importer do
       expect(compile_css("desktop"))
         .to include(":root{--font-family: #{base_font[:stack]}}")
         .and include(":root{--heading-font-family: #{heading_font[:stack]}}")
+
+      set_cdn_url("http://cdn.localhost")
+
+      # uses CDN and includes cache-breaking param
+      expect(compile_css("mobile"))
+        .to include("http://cdn.localhost/fonts/#{base_font[:variants][0][:filename]}?v=#{DiscourseFonts::VERSION}")
+        .and include("http://cdn.localhost/fonts/#{heading_font[:variants][0][:filename]}?v=#{DiscourseFonts::VERSION}")
     end
 
     it "includes all fonts in wizard" do