fix: remove decorator check in InvokableUserCommand

[shiftinv]

Summary

The sanity check for cases where both @command(default_member_permissions=) and @default_member_permissions() are used on the same callback was adjusted in #678.
Putting the @default_member_permissions() decorator below the application command decorator while also using Cog(..., *_command_attrs=...) (see example below) isn't supposed to throw an exception, and while this holds for @slash_command and @message_command, it didn't work with @user_command.

This makes all decorators work the same way.

Example:

class Misc(
    commands.Cog,
    user_command_attrs={"default_member_permissions": disnake.Permissions(32)},
):
    # this shouldn't raise.
    @commands.user_command()
    @commands.default_member_permissions(64)
    async def test(self, inter) -> None:
        await inter.send("pong!")

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, ...)