executor: make sure buildHashTable worker exits before IndexHashJoin finish (#31334)

[ti-srebot]

cherry-pick #31334 to release-5.4
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/31420

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git push git@github.com:ti-srebot/tidb.git pr/31420:release-5.4-40c0567ab398

---

What problem does this PR solve?

Issue Number: close #31062

Problem Summary:

What is changed and how it works?

Before this commit, buildHashTable worker may be still running while IndexHashJoin has finished already.
This commit makes the Close function wait for buildHashTable worker to exit to fix the problem.

Check List

Tests

Test

Side effects

N/A

Documentation

N/A

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• guo-shaoge
• wshwsh12

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[ti-srebot]

/run-all-tests

[ti-srebot]

@XuHuaiyu you're already a collaborator in bot's repo.

[VelocityLight]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: d3a70e7

[XuHuaiyu]

/merge

[ti-chi-bot]

@ti-srebot: Your PR was out of date, I have automatically updated it for you.

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