Statistics of global temporary table accumulates after commit

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

1. insert N records to a global temporary table and commit
2. check the row count in another session

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

estRows is 10000.0 or the row count in the current transaction.

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

estRows is N, which is the row count inserted.

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

master