client/tso: fix the bug that collected TSO requests could never be finished (#7951)

[ti-chi-bot]

This is an automated cherry-pick of #7951

What problem does this PR solve?

Issue Number: close #7849.

What is changed and how does it work?

If the `dispatcherCtx` is canceled, the collected `tsoRequest`s could be left unfinished forever,
which could cause the upper caller never to get the results. This PR fixed this bug by finishing them
on all the possible paths.

Check List

Tests

• Unit test
• Integration test

Release note

None.

[ti-chi-bot]

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[lhy1024]

Plz fix conflict

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick:

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