Update beautifulsoup4 to 4.11.1

`charset-normalizer` is now used by default if installed instead of
`chardet` (https://pyup.io/changelogs/beautifulsoup4/#4.11.0). We do
have `charset-normalizer` installed because it's a subdependency of the
requests library, so it is being used.

This caused the `test_content_too_long_returns_400` to fail since it
now thought that the encoding of `ŵ` is `{'encoding': 'Big5',
'language': 'Chinese', 'confidence': 1.0}`.

There are two options for fixing this
- change the test content so that it doesn't just contain a single
  letter - the docs state that you shouldn't run character detection on
  very tiny content
- add `chardet` as a requirement, so that the code functions exactly the
  same as before

I've chose the first option, since this avoids adding a dependency and
we should never have messages consisting of a single character.

requirements.in

@@ -22,7 +22,7 @@ SQLAlchemy==1.4.35
 strict-rfc3339==0.7
 rfc3987==1.3.8
 cachetools==5.0.0
-beautifulsoup4==4.10.0
+beautifulsoup4==4.11.1
 lxml==4.8.0
 Werkzeug==2.0.3