There are expensive "use xx" log when connection is high
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Description
## Bug Report
Please answer these questions before submitting your issue. Thanks!
### 1. Minimal reproduce step (Required)
use libmysqlclient C API in sysbench or use golang mysql driver
When the connection count is about 10k per tidb instance, there are many expensive "use xx" logs
```
[2024/12/27 03:16:18.596 +00:00] [WARN] [expensivequery.go:153] [expensive_query] [cost_time=60.025506506s] [conn=2162767018] [user=root] [txn_start_ts=0] [mem_max="0 Bytes (0 Bytes)"] [sql="use `sbtest`"] [session_alias=] ["affected rows"=0]
[2024/12/27 03:16:18.596 +00:00] [WARN] [expensivequery.go:153] [expensive_query] [cost_time=60.078729479s] [conn=2162766650] [user=root] [txn_start_ts=0] [mem_max="0 Bytes (0 Bytes)"] [sql="use `sbtest`"] [session_alias=] ["affected rows"=0]
```
### 2. What did you expect to see? (Required)
### 3. What did you see instead (Required)
### 4. What is your TiDB version? (Required)
master
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