statistics: fix "Invalid xxx character string" error when loading new collation stats (#36709)

[ti-srebot]

cherry-pick #36709 to release-6.2
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/36724

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

git push [email protected]:ti-srebot/tidb.git pr/36724:release-6.2-9cf1c34c54c1

---

What problem does this PR solve?

Issue Number: close #35208

What is changed and how it works?

#33146 didn't fix the loading new collation stats issues fully.

In this PR, we fix it again as we did in #27033.

Check List

Tests

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

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]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• qw4990
• winoros

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[ti-srebot]

/run-all-tests

[ti-srebot]

@time-and-fate you're already a collaborator in bot's repo.

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/525fb8cd839488cec3598ef707f2d081fc746b03

[time-and-fate]

/merge

[ti-chi-bot]

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

Commit hash: fdee2e1

[ti-chi-bot]

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