client/tso: fix the bug that collected TSO requests could never be finished

[JmPotato]

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]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• CabinfeverB
• HuSharp

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[HuSharp]

TestGetTSWhileRestingTSOClient ci failed :(

[JmPotato]

/merge

[ti-chi-bot]

@JmPotato: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

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

Commit hash: 51ad007

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #8089.