TIMESTAMP shouldn't shift timezone

[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 TIMESTAMP('2023-10-10T12:00:00Z');
+-----------------------------------+
| TIMESTAMP('2023-10-10T12:00:00Z') |
+-----------------------------------+
| 2023-10-10 12:00:00               |
+-----------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> select @@time_zone;
+-------------+
| @@time_zone |
+-------------+
| +08:00      |
+-------------+
1 row in set (0.04 sec)

3. What did you see instead (Required)

mysql> SELECT TIMESTAMP('2023-10-10T12:00:00Z');
+-----------------------------------+
| TIMESTAMP('2023-10-10T12:00:00Z') |
+-----------------------------------+
| 2023-10-10 20:00:00               |
+-----------------------------------+
1 row in set (0.00 sec)

mysql> select @@time_zone;
+-------------+
| @@time_zone |
+-------------+
| SYSTEM      |
+-------------+
1 row in set (0.00 sec)

SYSTEM is utc+8.

4. What is your TiDB version? (Required)

[zanmato1984]

/severity moderate