`FORMAT` has incorrect result

[YangKeao]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

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

mysql> SELECT FORMAT(1000/3, 5);
+-------------------+
| FORMAT(1000/3, 5) |
+-------------------+
| 333.33333         |
+-------------------+
1 row in set (0.01 sec)

3. What did you see instead (Required)

mysql> SELECT FORMAT(1000/3, 5);
+-------------------+
| FORMAT(1000/3, 5) |
+-------------------+
| 333.33330         |
+-------------------+
1 row in set (0.01 sec)

4. What is your TiDB version? (Required)

[zanmato1984]

/severity moderate