Investigate inconsistently-failing GatewayStaticAddresses conformance test

[bjee19]

GatewayStaticAddresses conformance test is failing inconsistently.

Here are two separate recent runs with the same failure:

• https://github.com/nginx/nginx-gateway-fabric/actions/runs/27307992104/job/80673276046?pr=5381#step:16:4002
• https://github.com/nginx/nginx-gateway-fabric/actions/runs/27309306331/job/80676386023#step:16:4034

I've verified locally that it does fail inconsistently. I believe it has to do with our recent changes in this PR: #5294.

Might be related to metallb and how we force certain ip addresses on the service loadbalancers. I had a hypothesis that if a separate Gateway already took the hardcoded usableGatewayIPAddress: 192.0.2.1 (since it is in the range of the metallb addresses:

apiVersion: metallb.io/v1beta1
kind: IPAddressPool
metadata:
  name: kind-pool
  namespace: metallb-system
spec:
  addresses:
  - 192.0.2.0-192.0.2.50

then perhaps the gateway-static-addresses gateway wouldn't be able to claim that ip address, and thus when the unusable address is removed in the test, it would error. However, I tried to reproduce this result locally and couldn't get it to error, seems like two gateways with metallb deployed can still have the same externalIP address.

AC:

• Test passes consistently.