SlashCommand.mention doesn't work for command groups

[tiltowait]

Summary

The SlashCommand.mention property does not create a proper mention when used in a command group.

Reproduction Steps

1. Create a command group
2. Inside the subcommand, output ctx.command.mention.

Minimal Reproducible Code

Within a cog:

group = SlashCommandGroup("group", "test group")

@group.command(name="command")
async def group_command(self, ctx):
    await ctx.respond(ctx.command.mention)

Expected Results

The response should have a mention to the command used.

Actual Results

The output is </group command:None>.

Intents

N/A

System Information

• Python v3.10.6-final
• py-cord v2.1.1-final
• aiohttp v3.8.1
• system info: Darwin 21.6.0 Darwin Kernel Version 21.6.0: Wed Aug 10 14:28:23 PDT 2022; root:xnu-8020.141.5~2/RELEASE_ARM64_T6000

Checklist

• [X] I have searched the open issues for duplicates.
• [X] I have shown the entire traceback, if possible.
• [X] I have removed my token from display, if visible.

Additional Context

No response

[JustaSqu1d]

Can confirm

[Makiyu-py]

wanted to tackle this issue but the bug seems to be already fixed on #1672