set abnormal value for tidb_enable_noop_variables don't report error or warning

[seiya-annie]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

mysql> SET global tidb_enable_noop_variables = 2;
Query OK, 0 rows affected (0.01 sec)

mysql> show global variables like '%tidb_enable_noop_variables%';
+----------------------------+-------+
| Variable_name              | Value |
+----------------------------+-------+
| tidb_enable_noop_variables | OFF   |
+----------------------------+-------+
1 row in set (0.00 sec)
mysql> show global variables like '%tidb_enable_noop_variables%';
+----------------------------+-------+
| Variable_name              | Value |
+----------------------------+-------+
| tidb_enable_noop_variables | OFF   |
+----------------------------+-------+
1 row in set (0.01 sec)

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

return error
ERROR 1231 (42000): Variable 'tidb_enable_noop_variables' can't be set to the value of '2'

3. What did you see instead (Required)

no error, no warning

4. What is your TiDB version? (Required)

| Release Version: v6.2.0
Edition: Community
Git Commit Hash: 65f7e2e
Git Branch: heads/refs/tags/v6.2.0
UTC Build Time: 2022-07-27 10:10:50
GoVersion: go1.18.2

[djshow832]

This also applies to other system variables, such as tidb_multi_statement_mode.
We need to modify them all at once.

[morgo]

This was fixed by #36647

ENUM variables can be specified by ordinal value as well (this is a MySQL compatible behavior). In latest master, it now only supports 0/1. Ideally, it should actually be changed to a TypeBool now. But that's a minor issue.