Add news attribute to TextChannel

[NeloBlivion]

Add the news attribute to TextChannel which implements is_news(), which in turn fixes the AttributeError raised in the base _TextChannel.__repr__ function.

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• If type: ignore comments were used, a comment is also left explaining why
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, typehinting, examples, ...)

[NeloBlivion]

The AttributeError referenced

Traceback (most recent call last):
  File "/home/container/.local/lib/python3.10/site-packages/discord/channel.py", line 190, in __repr__
    attrs = [(val, getattr(self, val)) for val in self._repr_attrs]
  File "/home/container/.local/lib/python3.10/site-packages/discord/channel.py", line 190, in <listcomp>
    attrs = [(val, getattr(self, val)) for val in self._repr_attrs]
AttributeError: 'TextChannel' object has no attribute 'news'

I'm not entirely sure if the approach with this change is appropriate; this is most comparable to is_nsfw() and nsfw existing alongside each other, however nsfw is an attribute that is_nsfw() returns, whereas this is the opposite case. The other options here are removing "news" from _repr_attrs, or appending it manually inside the __repr__ function.

[plun1331]

I would rather remove the news attr from _repr_attrs, as it doesn't really serve a purpose.
I'm not sure why is_nsfw ever existed, but removing it would be a breaking change.

[Dorukyum]

How about we add is_news to _repr_attrs instead?

[NeloBlivion]

How about we add is_news to _repr_attrs instead?

Just tried... you hit a max recursion depth error. For reference, this is how it's implemented in rc1

def __repr__(self) -> str:
    attrs = [(val, getattr(self, val)) for val in self._repr_attrs]
    joined = " ".join("%s=%r" % t for t in attrs)
    return f"<{self.__class__.__name__} {joined}>"

Whereas in b7, it was manually mapped

attrs = [
    ...
    ("news", self.is_news()),
    ... 
]

is_news isn't an attribute so trying this is guaranteed to fail. Though, I notice only TextChannel was updated to use this new method; all the other classes still manually map the attributes or just return the string without joining a list. Is there any reason for this?