lightning: don't ignore error if check new collation failed (#31089)

[ti-srebot]

cherry-pick #31089 to release-5.3
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/31152

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

git push git@github.com:ti-srebot/tidb.git pr/31152:release-5.3-9325c91a75d6

---

What problem does this PR solve?

Issue Number: close #31088

Problem Summary:

What is changed and how it works?

Do not ignore the error when execute query SELECT variable_value FROM mysql.tidb WHERE variable_name = 'new_collation_enabled', if the return err is sql.NORows, lightning will treat it as false, otherwise, directly return an error and exit.

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

Fix the error that if tidb-lightning doesn't has permission to access mysql.tidb, it will generate kv with wrong format.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• glorv
• kennytm

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[ti-srebot]

/run-all-tests

[ti-srebot]

@glorv you're already a collaborator in bot's repo.

[kennytm]

/merge

[ti-chi-bot]

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

Commit hash: 17442d2