lightning: always enable autocommit in db connection (#1114)

[ti-chi-bot]

This is an automated cherry-pick of #1114

What problem does this PR solve?

close #1104

What is changed and how it works?

Check List

Tests

• Integration test

Code changes

Side effects

Related changes

• Need to cherry-pick to the release branch

Release note

• Fix the bug that lightning tidb backend cannot load any data when autocommit is disabled.

[3pointer]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• 3pointer
• lance6716

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[glorv]

/merge

[ti-chi-bot]

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

Commit hash: 19d43f6

[lonng]

/merge