After the TiDB node crashes, login attempts fail

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

1. Use br(master-next-gen) restore db:
```bash
./br restore full --storage "s3://***/***" --pd "db-pd:2379" --send-credentials-to-tikv=true --checksum=false --keyspace-name=.... --checksum=false
```
2. Run the workload and wait for the tidb oom-killed
3. Reconnect the TiDB

Notice: The dataset is backuped on the v8.5.2 cluster.

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

Reconnect to the tidb

### 3. What did you see instead (Required)

ERROR 1045 (28000): Access denied for user 'root'@'10.*.*.*' (using password: YES)

### 4. What is your TiDB version? (Required)

["Welcome to TiDB."] [keyspaceName=xxxx] ["Release Version"=v9.0.0-beta.2.pre-342-g259852d] [Edition=Enterprise] ["Git Commit Hash"=259852d340d77be0fc95dbc2dcb1214bad18862f] ["Git Branch"=HEAD] ["UTC Build Time"="2025-08-18 13:48:38"] [GoVersion=go1.23.12] ["Race Enabled"=false] ["Check Table Before Drop"=false] ["Kernel Type"="Next Generation"] ["Enterprise Extension Commit Hash"=dc633aae52eb11b4e3549e3a7ef5b0ed14e159b1]