disttask: fix dispatcher cancel

[ywqzzy]

What problem does this PR solve?

Issue Number: close #45788

Problem Summary:

What is changed and how it works?

remove finishedTaskCh.

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

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[tiprow]

Hi @ywqzzy. Thanks for your PR.

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[hawkingrei]

/check-issue-triage-complete

[hawkingrei]

/ok-to-test

[codecov]

Codecov Report

Merging #45790 (2ec2653) into master (d43359a) will increase coverage by 0.0072%.
The diff coverage is 100.0000%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #45790        +/-   ##
================================================
+ Coverage   73.3540%   73.3612%   +0.0071%     
================================================
  Files          1271       1274         +3     
  Lines        393001     393674       +673     
================================================
+ Hits         288282     288804       +522     
- Misses        86354      86458       +104     
- Partials      18365      18412        +47     

Flag	Coverage Δ
integration	78.1388% <ø> (?)
unit	73.3529% <100.0000%> (-0.0011%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	54.0444% <ø> (ø)
parser	85.0359% <ø> (ø)
br	52.0441% <ø> (-0.0105%)	⬇️

[D3Hunter]

lgtm

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: D3Hunter, hawkingrei

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-08-04 03:51:57.214525973 +0000 UTC m=+416601.156874500: ☑️ agreed by D3Hunter.
• 2023-08-04 06:30:49.85307935 +0000 UTC m=+426133.795427880: ☑️ agreed by hawkingrei.