fix(render): transitive shader imports now work consistently on web (#19266)

# Objective

- transitive shader imports sometimes fail to load silently and return
Ok
- Fixes #19226

## Solution

- Don't return Ok, return the appropriate error code which will retry
the load later when the dependencies load

## Testing

- `bevy run --example=3d_scene web --open`


Note: this is was theoretically a problem before the hot reloading PR,
but probably extremely unlikely to occur.

crates/bevy_render/src/render_resource/pipeline_cache.rs

@@ -216,7 +216,11 @@ impl ShaderCache {
                     }
 
                     composer.add_composable_module(shader.into())?;
+                } else {
+                    Err(PipelineCacheError::ShaderImportNotYetAvailable)?;
                 }
+            } else {
+                Err(PipelineCacheError::ShaderImportNotYetAvailable)?;
             }
             // if we fail to add a module the composer will tell us what is missing
         }