sessionctx: fix var typo (#47609)

[ti-chi-bot]

This is an automated cherry-pick of #47609

What problem does this PR solve?

Issue Number: ref #45892

Problem Summary: fix typo

What is changed and how it works?

Check List

Tests

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

  • I checked and no code files have been changed.

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]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Defined2014, hawkingrei

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-10-25 06:29:38.528452231 +0000 UTC m=+2416176.115562360: ☑️ agreed by hawkingrei.
• 2023-10-25 06:30:48.122128356 +0000 UTC m=+2416245.709238501: ☑️ agreed by Defined2014.