fix backup stage order (#3910)

[ti-srebot]

cherry-pick #3910 to release-1.1
You can switch your code base to this Pull Request by using git-extras:

# In tidb-operator repo:
git pr https://github.com/pingcap/tidb-operator/pull/3913

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/tidb-operator.git pr/3913:release-1.1-63268cb2da3c

---

What problem does this PR solve?

Closes #3904

What is changed and how does it work?

Code changes

• Has Go code change
• Has CI related scripts change

Tests

• Unit test
• E2E test
• Manual test
• No code

Side effects

• Breaking backward compatibility
• Other side effects:

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release Notes

Please refer to Release Notes Language Style Guide before writing the release note.

[ti-srebot]

@liubog2008 please accept the invitation then you can push to the cherry-pick pull requests.
https://github.com/ti-srebot/tidb-operator/invitations

[handlerww]

LGTM

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• handlerww

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[handlerww]

/merge

[ti-chi-bot]

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

Commit hash: 99a3214