bug: Placement is not updated when the SyncTarget Heartbeat condition changes

[davidfestal]

Describe the bug

When the hearbeat condition of a SyncTarget changes (syncer started / stopped), this should impact placements which point to the location workspace containing this location.
That's not the case anymore on main.
That means that id a Syncer is started after KCP is running, and the SyncTarget becomes Ready, it will still not be taken in account by the placement scheduler.

Steps To Reproduce

1. Run KCP
2. Create a location workspace,
3. In the location workspace create a SyncTarget with the workload sync CLI command
4. Create a workload workspace and bind it to the location workspace with the bind compute CLI command
5. The placement created during bind will not be scheduled, and will have the No Valid SyncTargets message in the related condition.
6. Now start the syncer related to the Synctarget, and wait for the SyncTarget (in the location workspace) to be Ready
7. The Placement in the workload workspace should be updated and scheduled to the SyncTarget but it is not.

Expected Behaviour

When the hearbeat condition of a SyncTarget changes (syncer started / stopped), this should impact placements which point to the location workspace containing this location.

Additional Context

No response

[davidfestal]

I started observing this after the workspace refactoring.
@sttts any idea ?

[davidfestal]

cc @qiujian16