VIP doesn't switch when a TiProxy instance rejects connections

[djshow832]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. Deploy a cluster with VIP
2. The memory of the VIP leader is high and rejects connections
3. Still connect with the VIP

2. What did you expect to see? (Required)

Connections are estiblished

3. What did you see instead (Required)

Connections are rejected

4. What is your version? (Required)

v26.3.1