br/operator: fix adapt env for snapshot backup stuck when encountered error (#52607)

[ti-chi-bot]

This is an automated cherry-pick of #52607

What problem does this PR solve?

Issue Number: close #52049

Problem Summary:
When we failed to prepare the connections for wait apply, the channel may never be closed. Hence the pause PD operation (which relies on the finishing of the prepare connections stage) get stuck.

What changed and how does it work?

Selected over the context so it can be canceled.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  The change is almost trivial.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[ti-chi-bot]

@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/check_dev	5dfc70c	link	true	/test check-dev
idc-jenkins-ci-tidb/unit-test	5dfc70c	link	true	/test unit-test
idc-jenkins-ci-tidb/check_dev_2	5dfc70c	link	true	/test check-dev2
idc-jenkins-ci-tidb/build	5dfc70c	link	true	/test build

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[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:

1. It must be approved by the approvers firstly.
2. AFTER it has been approved by approvers, please wait for the cherry-pick merging approval from triage owners.

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