i18n: Merge similar translation strings in wp-admin/options.php

WARNING! is now Warning:

You have been warned.

Fixes #50715.
Props: ramiy, audrasjb, ocean90.


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git-svn-id: https://core.svn.wordpress.org/trunk@48332 1a063a9b-81f0-0310-95a4-ce76da25c4cd