cherrypick: fix lower case db name

[daviszhen]

What type of PR is this?

• API-change
• BUG
• Improvement
• Documentation
• Feature
• Test and CI
• Code Refactoring

Which issue(s) this PR fixes:

issue ##25079

What this PR does / why we need it:

修改 protected database lower case db name 问题

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[daviszhen]

@mergify refresh

[mergify]

refresh

✅ Pull request refreshed

[XuPeng-SH]

Re-checked the latest head. The previous blockers are fixed: protected_databases parsing no longer substitutes empty elements with the current database, and lower_case_table_names=2 is now treated consistently with the engine’s case-insensitive identifier semantics. The added unit/BVT coverage also pins those boundary cases, so I do not see a remaining correctness issue that should keep this blocked.