tests/tso: Create independent clients to prevent interfering with other tests.

[HuSharp]

What problem does this PR solve?

Issue Number: Ref #8103

What is changed and how does it work?

tests/tso: Create independent clients to prevent interfering with other tests.

Check List

Tests

• Integration test

Release note

None.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 77.62%. Comparing base (a766351) to head (a727a0d). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #8546 +/- ## ========================================== + Coverage 77.56% 77.62% +0.05% ========================================== Files 474 474 Lines 61861 61861 ========================================== + Hits 47981 48017 +36 + Misses 10347 10304 -43 - Partials 3533 3540 +7 ``` | [Flag](https://app.codecov.io/gh/tikv/pd/pull/8546/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tikv) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/tikv/pd/pull/8546/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tikv) | `77.62% <ø> (+0.05%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tikv#carryforward-flags-in-the-pull-request-comment) to find out more.

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lhy1024, okJiang

The full list of commands accepted by this bot can be found here.

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/tikv/pd/blob/master/OWNERS)~~ [lhy1024] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2024-08-20 03:12:12.261088166 +0000 UTC m=+235127.395538280: :ballot_box_with_check: agreed by lhy1024.
• 2024-08-20 07:36:00.530847971 +0000 UTC m=+250955.665298092: :ballot_box_with_check: agreed by okJiang.