config(pd): update pd-release-branch-pt to the correct chunk number

[JmPotato]

As https://github.com/tikv/pd/pull/6626 added 3 more chunks in the PD GitHub Actions workflow, this PR adopted this change for the release branches after release 7.3.

[ti-chi-bot[bot]]

Hi @JmPotato. Thanks for your PR.

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[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: wuhuizuo

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[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2024-05-10 02:53:38.179384111 +0000 UTC m=+1189771.936519687: :ballot_box_with_check: agreed by wuhuizuo.

[wuhuizuo]

/ok-to-test