Automatic merge from submit-queue (batch tested with PRs 51750, 53195, 53384, 53410). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

GCE: Handle missing subnet for legacy networks and auto networks with unique subnet names

Fixes #53409

/assign @bowei 

Tested on three GKE clusters with automatic, manual, and legacy networks.

**Release note**:
```release-note
GCE: Fixes ILB sync on legacy networks and auto networks with unique subnet names
```