auto update plugin not working

Testing #329614

I did
- For deterministic update testing, replace the marketplace repositories below with test forks containing an older installed plugin and a newer published version.
- made some changes and so there was not a newer version of the plugin
- had it as extensions.autoUpdate disabled, it didn't update
- turned it to extensions.autoUpdate enabled 🐛 and it still did not update

Start by reading issue #329614 and reproduce the deterministic update setup with marketplace test forks containing older installed and newer published plugin versions. Check behavior with extensions.autoUpdate disabled and enabled; done means the newer plugin is detected and installed when auto-update is enabled.

Written by the indexing model from the issue text.