Fix DATATIME typo and precision/scale wording

[yahonda]

What is changed, added or deleted? (Required)

• sql-mode.md: fixes a typo, DATATIME → DATETIME, in the ALLOW_INVALID_DATES mode description.
• tidb-troubleshooting-map.md: DECIMAL(a, b) uses a for precision and b for scale; the text called both "the target precisions".

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

• master (the latest development version)
• v9.0 (TiDB 9.0 versions)
• v8.5 (TiDB 8.5 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)

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

• This PR is translated from:
• Other reference link(s): found while reviewing CodeRabbit feedback during Japanese translation review of i18n(ja): remove stray brace artifacts and fix accompanying word-order swaps #23699

AI agent involvement

• The changes in this PR were primarily made by an AI agent on behalf of the PR author.

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

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📥 Commits

Reviewing files that changed from the base of the PR and between 0dc31ea and 0c3a2d8.

📒 Files selected for processing (2)

• sql-mode.md
• tidb-troubleshooting-map.md

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