i18n(ja): fix broken multiplication-sign spacing in cost-model.md

[yahonda]

What is changed, added or deleted? (Required)

Fixes a regression introduced by #23602's automated MD037 (no-space-in-emphasis) fix: it misidentified the literal multiplication asterisk in the index-cost formula as Markdown emphasis markup and stripped the surrounding spaces, turning 20 * 8 into 20* 8.

This escapes the first asterisk in each formula (\*), matching how the English source (cost-model.md) already escapes it, so markdownlint no longer treats it as emphasis while keeping the formula readable.

Found while reviewing/rebasing PR #23594.

Which TiDB version(s) do your changes apply to? (Required)

• i18n-ja-release-8.5 (TiDB Japanese documentation for TiDB 8.5 versions)

What is the related PR or file link(s)?

• Other reference link(s): regression introduced by i18n(ja): fix markdownlint conformance (MD030/046/037/022/032/039/034/012) to match release-8.5 #23602

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

Summary by CodeRabbit

• Documentation
  • Improved formatting and consistency in index cost calculation examples.
  • Clarified multiplication symbols and spacing without changing the calculations or explanations.

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 9ef6b6f and 5159562.

📒 Files selected for processing (1)

• cost-model.md

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📝 Walkthrough

Walkthrough

インデックス b と c のコスト計算式で、乗算記号と空白表記を修正しました。計算値と説明内容は変更していません。

Changes

インデックスコスト計算例

Layer / File(s)	Summary
コスト計算式の表記修正 cost-model.md	インデックス b と c の計算式の乗算記号と空白表記を修正しました。

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk: ⚪ Minimal · up to 51595

This localized documentation change restores readable multiplication-sign spacing without introducing actionable merge-blocking risk; it is merge-ready after normal checks and review.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description explains the regression, identifies the fix, specifies the affected Japanese 8.5 documentation version, and includes a related reference. Optional checklist sections are omitted, but t…
Title check	✅ Passed	The title clearly and concisely describes the main change: fixing multiplication-sign spacing in the Japanese cost-model documentation.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description explains the regression, identifies the fix, specifies the affected Japanese 8.5 documentation version, and includes a related reference. Optional checklist sections are omitted, but the required content is complete.

Full details: Docstring Coverage

Explanation

No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0 files. (1 skipped: 1 unsupported.)

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-08-26 02:47:22.011738469 +0000 UTC m=+642677.182832601: ☑️ agreed by qiancai.