Database: Send a 500 status and no-cache headers when using db-error.php or maintenance.php drop-ins

[dineshinau]

Due to an PHPCS error in PR: #13471, creating a new PR after fixing the errors using phpcbf

Trac ticket: https://core.trac.wordpress.org/ticket/66080

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[github-actions]

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[github-actions]

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[westonruter]

Not sure why this second PR is needed. Closing in favor of keeping all the work on the previous PR: #13471