[next-gen on clould] add index still succeeded when tidb cannot communicate with tikv workers

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)
1、there was no tikv worker config in tidb
2、run add index

### 2. What did you expect to see? (Required)
add index failed

### 3. What did you see instead (Required)
add index still succeeded when tidb cannot communicate with tikv workers


### 4. What is your TiDB version? (Required)
sh-5.1# ./tidb-server -V
Release Version: v9.0.0-nextgen
Edition: Community
Git Commit Hash: 2dce92429d784d75c94146638c3ac1e437e859c8
Git Branch: heads/refs/tags/v9.0.0-nextgen
UTC Build Time: 2025-05-19 08:16:50
GoVersion: go1.23.9
Race Enabled: false
Check Table Before Drop: false
Store: unistore
Kernel Type: Next Generation

sh-5.2# ./tikv-server -V
TiKV
Release Version: 8.5.0
Edition: Cloud Storage Engine
Git Commit Hash: 9e6a8cd610da48825ac057fdfaedc0926da3b2af
Git Commit Branch: refs/heads/write-sst
UTC Build Time: 2025-05-16 08:25:38
Rust Version: rustc 1.77.0-nightly (89e2160c4 2023-12-27)
Enable Features: pprof-fp jemalloc mem-profiling portable test-engine-kv-rocksdb test-engine-raft-raft-engine cloud-aws cloud-gcp cloud-azure
Profile: release