memory_quota hint should be extracted for Union

[jackysp]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. create a table like sysbench tables, insert 1M rows.

select /*+ memory_quota(1 MB) */ id from sbtest1 where k > 1 union all select id from sbtest1 where k > 0;

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

Memory quota exceeded.

3. What did you see instead (Required)

No error.
The following SQL works

select /*+ memory_quota(1 MB) */ * from (select /*+ memory_quota(1 MB) */ id from sbtest1 where k > 1 union all select id from sbtest2 where k > 0)

4. What is your TiDB version? (Required)

From v6.5 to v7.5

[hawkingrei]

I think it has been fix by #50068 and #50067