Hide 'Database Upgrade Required' on admin/network/upgrade.php when you are not being asked to upgrade, to prevent confusion.

Merges [25191] to the 3.6 branch.

props duck_.
fixes #24845.


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Case sensitivity for is_email_address_unsafe().

Merges [25197] to the 3.6 branch.

props jkudish.
fixes #25046.

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