bpo-30629: Fix call lower() twice

[narusemotoki]

https://bugs.python.org/issue30629
https://github.com/python/cpython/blob/master/Lib/html/parser.py#L415

        elem = match.group(1).lower() # script or style
        if self.cdata_elem is not None:
            if elem != self.cdata_elem:
                self.handle_data(rawdata[i:gtpos])
                return gtpos

        self.handle_endtag(elem.lower())

elem is lowercase string because lower() is called at the first line.
So the last line of calling lower() is unnecessary.

[mention-bot]

@narusemotoki, thanks for your PR! By analyzing the history of the files in this pull request, we identified @ezio-melotti, @freddrake and @bitdancer to be potential reviewers.

[the-knights-who-say-ni]

Hello, and thanks for your contribution!

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[narusemotoki]

@rhettinger @the-knights-who-say-ni
Hello
Now, I can see "Contributor Form Received Yes" on my profile page. How can I run CLA check again or Could I ask you to do it?