migrate-from-mysql-using-aws-dms: fix "test" mislabeled as a system database

[yahonda]

What is changed, added or deleted? (Required)

The doc listed test alongside INFORMATION_SCHEMA, PERFORMANCE_SCHEMA, mysql, and sys under the label "system databases". test is a default user database TiDB/MySQL creates for convenience, not a system (metadata) database like the other four. Reworded the shared label to "default databases", which accurately covers all five entries without changing the practical guidance (still filter out all five when setting up an AWS DMS migration task).

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

• master (the latest development version)
• v8.5 (LTS)

Do your changes match any of the following descriptions? (Required)

• Delete files in the markdown-pages repository
• Change the directory
• Need modification after machine translation
• Screenshots or GIFs are included in the changes

Summary by CodeRabbit

• Documentation
  • Updated the AWS DMS migration guide to recommend explicitly selecting only the databases and tables intended for migration.
  • Clarified that using the default % wildcard may include MySQL system databases and cause the migration task to fail.

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📝 Walkthrough

Walkthrough

The AWS DMS migration guide now instructs users to select only the databases and tables they want to migrate. It warns that the default % wildcard can include MySQL system databases and cause the migration task to fail.

Changes

AWS DMS documentation

Layer / File(s)	Summary
Migration task selection guidance tidb-cloud/migrate-from-mysql-using-aws-dms.md	Updates the prerequisite to recommend explicit database and table selection. The guidance lists system databases that the % wildcard might migrate and identifies possible task failure.

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

Merge Risk: 🔵 Low · up to b4e5b

The AWS DMS guide changes database-selection guidance, but an unresolved terminology inconsistency could confuse users about which default databases must be excluded. Resolve the wording before merge.

Suggested reviewers: qiancai

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main documentation change: correcting the classification of test as a system database.
Description check	✅ Passed	The description explains the change, its rationale, affected TiDB versions, and applicable change categories. It omits some optional template sections, but the required information is complete.
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.

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[qiancai]

/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qiancai

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch master: #23756.