Correct example ActiveStorage fixture file path

There are similar example in [File Attachment Fixtures]

```
# test/fixtures/active_storage/blobs.yml
...
# test/fixtures/active_storage/attachments.yml
...
```

[File Attachment Fixtures]: https://edgeguides.rubyonrails.org/testing.html#file-attachment-fixtures

Author: choznerol

guides/source/active_storage_overview.md

@@ -1322,15 +1322,15 @@ test.
 Next, create fixture files for the Active Storage classes:
 
 ```yml
-# active_storage/attachments.yml
+# test/fixtures/active_storage/attachments.yml
 david_avatar:
   name: avatar
   record: david (User)
   blob: david_avatar_blob
 ```
 
 ```yml
-# active_storage/blobs.yml
+# test/fixtures/active_storage/blobs.yml
 david_avatar_blob: <%= ActiveStorage::FixtureSet.blob filename: "david.png", service_name: "test_fixtures" %>
 ```