Since 3.16.x store subscriptions don't seem to work at all if value is changed within an action

[antony]

Describe the bug
Apologies for the terrible naming. I discovered this bug when my site broke, and after trying to discover a workaround, I think the problem is worse than I initially thought.

It seems that since 3.16.x, store auto subscriptions are quite broken, if their value is updated by an action.

To Reproduce
@dkondrad has a simplified example here which doesn't work all the way back to 3.10.x:

https://svelte.dev/repl/4a75f39e16c44fccb48104e857d21a50?version=3.16.3

Expected behavior
Stores should be autosubscribed and values updated when they change.

Information about your Svelte project:

• Svelte version 3.16.3, 3.16.2, 3.16.1

Severity
Severe. I can't find a workaround for this, and it appears that auto-subscriptions are completely broken.

Additional Notes

I don't know if this relates to #4081 - but it seems suspect.

[ghost]

Still broken with this repl:
https://svelte.dev/repl/5239a903de1b401f92113318dcb344cc?version=3.16.4

Seems action is triggered after the update, though that's exactly what the docs say so not sure if really should even work in the first place.