docs: fix incorrect column references in AGG_STATE example

[dewanshshekhar]

The AGG_STATE example in zh-CN/docs/2.1/table-design/data-model/aggregate.md was using non-existent columns k2 and k3, which do not match the table schema.

Updated the example queries to use the correct columns v1 and v2:

insert into aggstate select 3,sum(v1),group_concat_union(v2) from aggstate;

select sum(v1), group_concat_merge(v2) from aggstate;

select sum(v1), group_concat_merge(v2) from aggstate where k1 != 2;

## Versions 

- [ ] dev
- [ ] 3.0
- [ ] 2.1
- [ ] 2.0

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