The execution plan performance is inconsistent in prepare and non-prepare modes, under different collation

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

```

### 2. What did you expect to see? (Required)
Consistent execution plan when using hint
### 3. What did you see instead (Required)

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

MySQL [test]> SELECT tidb_version();
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()
|
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v6.0.0-8-g9258e39-dirty
Edition: Community
Git Commit Hash: 9258e39482be50fce59758ccb9ed0a03c010b225
Git Branch: release-6.0
UTC Build Time: 2022-06-05 08:54:27
GoVersion: go1.18
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false