[improvement](test) add sync for test_agg_keys_schema_change_datev2

[morningman]

Proposed changes

Issue Number: close #xxx

Problem summary

1. add "sync" to avoid some potential meta sync problem when running regression test on multi-node cluster
2. Use /tmp dir as dest dir of outfile test, to avoid "No such file or directory" error.

Checklist(Required)

1. Does it affect the original behavior:
   • Yes
   • No
   • I don't know
2. Has unit tests been added:
   • Yes
   • No
   • No Need
3. Has document been added or modified:
   • Yes
   • No
   • No Need
4. Does it need to update dependencies:
   • Yes
   • No
5. Are there any changes that cannot be rolled back:
   • Yes (If Yes, please explain WHY)
   • No

Further comments

If this is a relatively large or complex change, kick off the discussion at dev@doris.apache.org by explaining why you chose the solution you did and what alternatives you considered, etc...

[Gabriel39]

LGTM