Extend custom CSS cache time with digest paths (#33207)

config/initializers/settings_digests.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+Rails.application.config.to_prepare do
+  custom_css = begin
+    Setting.custom_css
+  rescue ActiveRecord::AdapterError # Running without a database, not migrated, no connection, etc
+    nil
+  end
+
+  if custom_css.present?
+    Rails
+      .cache
+      .write(
+        :setting_digest_custom_css,
+        Digest::SHA256.hexdigest(custom_css)
+      )
+  end
+end