planner/core: fix the 'for update' condition for the point get query (#11771)

[sre-bot]

cherry-pick #11771 to release-3.0

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What problem does this PR solve?

Fix bug introduced in #11715

Sometimes, InTxn() is not precise, so we should check both InTxn() and autocommit

// We should set the 'for update' flag in this case.
set @@auto_commit = 0;
select * from t where id = 6 for update;  // This is not InTxn() when the planner run here, because it's still in the plan phase.

What is changed and how it works?

The check condition is changed from InTxn() to IsAutocommit() || InTxn()

Check List

Tests

• Unit test
• Manual test (add detailed scripts or steps below)

Related changes

• Need to cherry-pick to the release branch

[sre-bot]

/run-all-tests

[jackysp]

LGTM

[coocood]

LGTM