Prevent WP_Tag_Processor::set_modifiable_text() from allowing SCRIPT contents with "<script" like it does with "</script". Either of these sequences may affect the script element's close. Developed in https://github.com/WordPress/wordpress-develop/pull/9560. Props jonsurrell, westonruter, dmsnell. See #63738. Built from https://develop.svn.wordpress.org/trunk@60706 git-svn-id: http://core.svn.wordpress.org/trunk@60042 1a063a9b-81f0-0310-95a4-ce76da25c4cd