cluster: fix tso fallback when pd leader switch (#8783)

[ti-chi-bot]

This is an automated cherry-pick of #8783

What problem does this PR solve?

Issue Number: Close #8781

What is changed and how does it work?

Check List

Tests

• Unit test

Release note

None.

[codecov[bot]]

Codecov Report

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

Please upload report for BASE (release-8.5@649393a). Learn more about missing BASE report.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## release-8.5 #8784 +/- ## ============================================== Coverage ? 75.71% ============================================== Files ? 461 Lines ? 72281 Branches ? 0 ============================================== Hits ? 54724 Misses ? 14055 Partials ? 3502 ``` | [Flag](https://app.codecov.io/gh/tikv/pd/pull/8784/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/8784/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tikv) | `75.71% <100.00%> (?)` | | 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: okJiang, rleungx

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/tikv/pd/blob/release-8.5/OWNERS)~~ [rleungx] 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:

• 2024-11-07 07:03:46.440158979 +0000 UTC m=+1110939.279314575: :ballot_box_with_check: agreed by rleungx.
• 2024-11-07 07:20:07.35826316 +0000 UTC m=+1111920.197418706: :ballot_box_with_check: agreed by okJiang.