Setting global variables for GC configuration may reports confusing error message

[MyonKeminta]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

set @@global.tidb_gc_life_time = '1m0s';

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

TiDB reports the value is too small (shorter than 10m, the minimum allowed GC life time), or maybe it's also acceptable that TiDB automatically adjust the value to 10m. (I personally prefer the former)

3. What did you see instead (Required)

ERROR 1232 (42000): Incorrect argument type to variable 'tidb_gc_life_time'

The error message is confusing, and a user may be unable to understand what's going wrong.

4. What is your TiDB version? (Required)

master