executor: fix goroutine leak in querying slow log (#32757)

[ti-srebot]

cherry-pick #32757 to release-5.4
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/32782

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/tidb.git pr/32782:release-5.4-62ec7468e738

---

What problem does this PR solve?

Issue Number: close #32656

Problem Summary:

goroutine leaks in parseSlowLog when the query is canceled.

What is changed and how it works?

Check context when waiting for the channel.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

[ti-chi-bot]

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[ti-srebot]

/run-all-tests

[ti-srebot]

@djshow832 you're already a collaborator in bot's repo.

[ti-chi-bot]

@ti-srebot: PR needs rebase.

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[tiancaiamao]

Please resolve conflict @djshow832

[djshow832]

This PR conflicts because a previous fix was merged into release-5.4: https://github.com/pingcap/tidb/pull/33961/files#diff-9cb39ec0c8d4960b6e8f64d27731000897c8296503bad061a574b3dd8ac17c11, which contains this fix.
So I don't need to merge this PR now.

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/1d5bae318a9673316f41c6bfeeb5cedb652c78d3