Fixing implicit parser name for Beautiful Soup (lms, openedx)

Description

Fixing 56 GuessedAtParserWarnings, in commit edx#24098

*Background*: BeautifulSoup automatically picks the fastest parser available. By default, it picks the "lxml" parser.

Per the [BeautifulSoup](https://www.crummy.com/software/BeautifulSoup/bs4/doc/#installing-a-parser) documentation:

> Beautiful Soup supports the HTML parser included in Python’s standard library, but it also supports a number of third-party Python parsers. One is the lxml parser. Depending on your setup, you might install lxml with one of these commands.
> Another alternative is the pure-Python html5lib parser, which parses HTML the way a web browser does.

*Context*: We changed two statements in lms and another in openedx. The statements fire up BeautifulSoup. Now we explicitly ask for "lxml," following the recommendation on BeautifulSoup's documentation:
> If you can, I recommend you install and use lxml for speed. If you’re using a very old version of Python – earlier than 2.7.3 or 3.2.2 – it’s essential that you install lxml or html5lib. Python’s built-in HTML parser is just not very good in those old versions.

*Before*:
`soup = BeautifulSoup(response.content)`

*After*:
`soup_html = BeautifulSoup(markup=content, features="lxml")`

The warnings are gone, tests are passing in local.

@felipemontoya
@Alec4r

Assignee

Jeremy Bowman

Reporter

Open Source Pull Request Bot

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Daniel Francis

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edx/edx-platform

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