<SCRIPT> tag in uppercase incorrectly generates error

Reported on Zendesk:

> When a student opens the `` tag, they automatically are given a closing script tag `` that matches the case they entered:
>
> `
> `
>
> The upper case closing tag `` immediately generates the error message
>
> "It looks like your `` tag never closes."
>
> The parser does not appear to accept upper case closing tag ``

Replicated, example can be seen on [this project](https://www.khanacademy.org/computer-programming/uppercase-script-tag-error/5220028773695488).

All caps would still be valid HTML for the`` tag, so this should be accepted.

Reproduce the uppercase case in the linked Khan Academy project, then trace the live editor's HTML parsing and unclosed-tag error path. Done means matching uppercase opening and closing script tags are accepted without the error message.

Written by the indexing model from the issue text.