hash agg parallel spill get wrong result

[windtalker]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

for a simple query like

select count(*), id from t group by id

if parallel spill is triggered, it will return wrong result.

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

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

[xzhangxian1008]

/assign