Make tests less noisy (#12463)

When running the tests for linux, I found a lot of benign errors getting
logged. This PR cuts down some of the noise from unnecessary workspace
serialization and SVG renders

Release Notes:

- N/A

crates/theme_importer/src/assets.rs

@@ -11,10 +11,11 @@ use rust_embed::RustEmbed;
 pub struct Assets;
 
 impl AssetSource for Assets {
-    fn load(&self, path: &str) -> Result<Cow<'static, [u8]>> {
+    fn load(&self, path: &str) -> Result<Option<Cow<'static, [u8]>>> {
         Self::get(path)
             .map(|f| f.data)
             .ok_or_else(|| anyhow!("could not find asset at path \"{}\"", path))
+            .map(|result| Some(result))
     }
 
     fn list(&self, path: &str) -> Result<Vec<SharedString>> {