fix(commands): handle interactions in union types correctly

[shiftinv]

Summary

Changes the lenient issubclass_ we're using for parts of slash parsing to also support issubclass_(X[T], X), instead of using issubclass_(get_origin(...), ...).
This fixes cases where the interaction annotation is a Union, which worked fine before #1037 where I missed this in review.

Code

@bot.slash_command()
async def test(inter: Union[disnake.ApplicationCommandInteraction, commands.Context]) -> None:
    ...

#   File "disnake/ext/commands/params.py", line 766, in parse_annotation
#     raise TypeError(
# TypeError: Unions for anything else other than channels or a mentionable are not supported

Checklist

• If code changes were made, then they have been tested
  • I have updated the documentation to reflect the changes
  • I have formatted the code properly by running pdm lint
  • I have type-checked the code by running pdm pyright
• 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, ...)