planner: fix incorrect estCost displayed in explain results

[qw4990]

What problem does this PR solve?

Issue Number: close #32672

Problem Summary: planner: fix incorrect estCost displayed in explain results

What is changed and how it works?

planner: fix incorrect estCost displayed in explain results

This only fixes estCost displayed in explain results and won't affect costs used for plan selection.

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

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Reminiscent
• time-and-fate

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[3AceShowHand]

LGTM

[qw4990]

/merge

[ti-chi-bot]

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

Commit hash: 21fe2fa

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/4e176af634a3cdb6521cf4bd19bf5405f38c2d61

[qw4990]

/merge

[sre-bot]

Please follow PR Title Format:

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Or if the count of mainly changed packages are more than 3, use

• *: what is changed

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[qw4990]

/merge

[qw4990]

/merge

[ti-chi-bot]

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