fix(assets): replace .gif asset format to webp for animated assets

[SilberGecko6917]

Summary

This PR changes the .gif asset extention for avatars, banners and other images to the .webp extention.

https://docs.discord.com/developers/reference#image-formatting

I noticed that if a user had an animated profile picture, the URL of the image returned a 415 Unsupported Media Type error. For example, here:
https://cdn.discordapp.com/guilds/1010915072694046794/users/851762178532311050/avatars/a_8a63bc5a3a227954876eb04778006c13.gif?size=1024

but with webp it works:
https://cdn.discordapp.com/guilds/1010915072694046794/users/851762178532311050/avatars/a_8a63bc5a3a227954876eb04778006c13.webp?animated=true&size=1024

Information

• 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, ...).

Checklist

• I have searched the open pull requests for duplicates.
• 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.
• I have updated the changelog to include these changes.
• AI Usage has been disclosed.
  • If AI has been used, I understand fully what the code does

[pycord-app]

Thanks for opening this pull request!
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This pull request can be checked-out with:

git fetch origin pull/3294/head:pr-3294
git checkout pr-3294

This pull request can be installed with:

pip install git+https://github.com/Pycord-Development/pycord@refs/pull/3294/head