[BUG] Fix sync cog_unload method of MonthlyYappathon Cog

[Jiggly-Balls]

Describe the bug

Not a major bug but the cog_load method in src.bot.cogs.features.MonthlyYapathon cog is sync which can potentially case problems.

Expected behavior

The cog must be defined as an async method to function properly.

To Reproduce

None.

Screenshots

None.

How was the bot ran

make start

Additional context

None.